Laura Adams, Curriculum Developer – NAFTC
This article is one of two articles that will appear in the coming months that will provide a basic overview of electric drive vehicle infrastructure. This article will review electric vehicle supply equipment (EVSE) and levels of charge in electric drive vehicles. An upcoming article will cover EVSE mounting styles, EVSE placement, and the collective roles of service personnel involved in EVSE installation.
Consumers and fleets that drive plug-in hybrid electric vehicles (PHEVs) and battery electric vehicles (BEVs) need a well-developed infrastructure of electric vehicle supply equipment to charge their electric vehicles. It is important that drivers have access to convenient options for charging their vehicles at home, work, or in public places. Electric vehicle supply equipment, or EVSE, refers to the fixtures outside of the electric vehicle that provide the electricity needed to charge the vehicle’s battery. The following will review the main components of EVSE.
Electric Vehicle Supply Equipment
Electric vehicle supply equipment, or EVSE, is the general term used for all of the equipment that supplies electricity to electric vehicles. By definition from the National Electric Code, electric vehicle supply equipment includes the conductorsincluding the ungrounded, grounded, and equipment grounding conductorsand the electric vehicle connectors, attachment plugs and other fittings, devices, power outlets, or apparatuses installed specifically for the purpose of transferring energy between the premise wiring and the electric vehicle. EVSE is installed specifically for the purpose of delivering electricity from a designated power source to the electric vehicle for charging. EVSE establishes communication and transfers power to the electric vehicle while providing proper grounding, shock protection, overload protection, and general safety during the charging process.
An EVSE unit is the main device that is mounted to a wall, pole, pedestal, or ceiling which is connected to an external power source. Each EVSE unit has specific installation requirements that call for specific voltages, amperages, wiring sizes, and optional networking capabilities that are specific to the charging location. Connected to the EVSE unit are the EV cord and the EV connector, which safely transfer electricity to the electric vehicle’s inlet.
This ChargePoint Public Charging Station is an example of an EVSE unit. Credit: NAFTC.
The EV cord is an off-board cable which carries electrical current from the EVSE unit to the EV connector, which then plugs into the vehicle’s inlet. This cord also sends communication signals between the EVSE unit and the EV connector during the energy transfer.
The EV connector refers to the plug in end of the EV cord, which transfers electricity from the EVSE unit to the electric vehicle. The EV connector is inserted into the EV inlet located on the electric vehicle; this establishes an electrical connection to the vehicle for the purposes of energy transfer and information exchange.
There are three common types of EV connectors that are in use today. For Level 1 and Level 2 charging, the industry standard for the EV connector is the Society of Automotive Engineer’s J1772. The Society of Automotive Engineers, or SAE, standardized the J1772 connector for safety and durability. The J1772 was also standardized for uniformity so that different models of electric vehicles could all use the same connector for Level 1 and Level 2 charging. There is a dedicated EV inlet that serves the SAE J1772 connector on both PHEVs and BEVs.
SAE J1772 Connector serves both Level 1 and Level 2 charging. Credit: NAFTC.
For Level 3 charging or fast charging, there are two different types of EV connectors: the Chademo connector and the SAE J1772 Combo connector. The levels of charging are described in greater detail below. The Chademo connector has been the incumbent standard for Level 3 charging. It was developed several years ago by the Tokyo Electric Power Company and Japanese automakers. The Level 3 Chademo connector requires a different physical plug than the Level 1 and Level 2 SAE J1772 connector and requires a different inlet.
Chademo connector serves Level 3 charging. Credit: NAFTC.
The SAE J1772 Combo connector is a new iteration of the J1772 standard. The Combo was developed by American makers who wanted to have one plug that was capable of serving the needs of Level 1 and Level 2 charging as well as Level 3 fast charging.
Although the Chademo and J1772 Combo are both Level 3 connectors, they are not compatible with each other and require different dedicated EV inlets. The Level 3 connectors currently serve only battery electric vehicles. The EV connector is one part of the EV coupler system which combines the EV connector to the EV inlet.
Electric vehicles have dedicated inlets to serve the three different types of EV connectors. The EV inlet is the device on the electric vehicle in which the EV connector is inserted. The Level 1 and Level 2 SAE J1772 connector, Level 3 Chademo connector, or SAE J1772 Combo connector is inserted to allow the transfer of power and communication.
Car charging inlet with Chademo connector on left and J1772 on right allows for two levels of charging. Credit: NAFTC.
Three Different Levels of Charge
EVSE is classified into three different levels by the rate at which the equipment charges the electric vehicle’s battery. These levels are identified as Level 1, Level 2, and Level 3. The rate at which the EVSE charging adds range or miles to a electric vehicle, among the three different levels of charge, depends on the electric vehicle, the battery type, and the EVSE’s level of charge. The following will review the three different levels of charge.
Level 1 Charging
Level 1 EVSE provides charging through a 120 volt, alternate current, or AC, receptacle. At this charging level, equipment can operate at up to 15 to 20 amperes and will require a dedicated 20 to 25 amp circuit. Typically, homes already have 120 volt receptacles installed, but for EV charging, the receptacle must be a dedicated circuit. Most, if not all, PHEVs and BEVs will come with a Level 1 EVSE portable cord set that can be kept with the vehicle at all times. The Level 1 charging unit requires no additional charging equipment and can be used when the driver is running low on charge on the road and needs to plug into a readily available outlet.
To use the Level 1 EVSE, the driver will take one end of the Level 1 EVSE cord, which is a standard, three-prong, NEMA 5-15 plug, and plug that into a 120 volt receptacle. The driver will then take the other end of the Level 1 EVSE cord, which is the SAE J1772 standard connector, and plug it into the electric vehicle’s inlet. For Level 1 charging, based on the battery type of the electric vehicle, the rate of charge adds about two to five miles of range to the vehicle per hour of charging time.
Level 2 Charging
Level 2 EVSE provides charging through a 240 volt, alternate current, or AC, receptacle. Level 2 EVSE requires the installation of home, public, or fleet charging equipment and a dedicated circuit of 30 to 80 amps requiring 40 to 100 amp circuit. As this charging option can operate at up to 80 amperes, which would be adequate, most residential Level 2 EVSE will operate at lower power. Many such units operate at up to 30 amperes requiring a dedicated 40 amp circuit. Most homes have 240 volt service available, and because Level 2 EVSE can easily charge a typical EV battery overnight, this will be a common installation for homes. Level 2 EVSE units are typically installed on a wall, floor, ceiling, or on a pedestal. Level 2 EVSE also uses the standard SAE J1772 connector to plug into the vehicle inlet.
To use the Level 2 EVSE, the charging unit may be either plugged into a 240 volt receptacle or hardwired to a dedicated circuit. The driver will take the SAE J1772 standard connector, and plug it into the vehicle. For Level 2 charging, the rate of charge adds about 10 to 20 miles of range to the vehicle per hour of charging time, based on the battery type of the electric vehicle and circuit capacity. Level 2 is typically used for charging at home and public locations. The driver can conveniently charge the vehicle at home while sleeping or in a public location while at work or shopping. This convenient charging regimen is often called opportunity charging, because it calls for recharging during “opportune” down time such as sleep, work, or play.
Level 3 Charging
Level 3 EVSE provides off-board charging of 400 volts to 600 volts of direct current, or DC. Level 3 charging is commonly referred to as “DC Charging” or “Fast Charging.” Instead of taking hours to charge, the fast charge takes only minutes. Currently, the exact voltage and load specifications for Level 3 charging have not been defined. With the amount of electrical power supplied through Level 3 charging, it is viewed as the electric vehicle’s equivalent to the commercial gas station. It can provide nearly 80% of a full charge in less than 30 minutes.
Currently, battery electric vehicles, such as the Nissan Leaf and the Mitsubishi iMiev, are equipped to accept Level 3 charging with the use of a Chademo connector. For Level 3 charging, the rate of charge adds 60 to 80 miles of range to the vehicle in 20 to 30 minutes of time. With the need for very little recharging downtime, Level 3 charging has been considered for the use of fleet vehicles as well as ideal for public charging. Drivers can conveniently access the charging station and quickly charge their vehicle.
Comparison of Levels 1, 2, and 3 rate of charge. Credit: NAFTC.
As a continuation of previous articles on the National Alternative Fuels Training Consortium pilot Electric Drive Vehicle Automotive Technician course, we will be documenting various lab activities from the course, and the results gained from the recently held train-the-trainer session. The shop task represented here will be the safe removal of the high-voltage battery pack from a hybrid electric vehicle.
Through work with industry and academic partners, the NAFTC was able to offer our participants a variety of vehicles to work with, representing Toyota, Ford, Lexus, and Chevrolet. Representing by far the most prevalent electric drive vehicle on our highways today, this shop activity focused on the high-voltage battery pack in the 3rd generation Toyota Prius.
Students shown are using Toyota factory scan tools in preparation for a shop activity during the NAFTC’s Electric Drive Vehicle Automotive Technician course. Credit: NAFTC.
To best promote individual effort while simultaneously emphasizing teamwork, students were grouped into teams of four and assigned their own car for the hands-on portion of the course, including this task of battery removal. In each group of four, the team assigned individuals specific responsibilities to perform in each task. This activity required someone to be appointed as a high-voltage safety specialist, another as a data recorder, another as an illustrator, and the fourth to be in charge of disassembly/assembly.
Each team selected the best person within the group for each responsibility based on skill and interest. Through the steps of disabling the vehicle, isolation of high voltage, removal of the battery pack, diagnostics and testing of the battery pack, illustration of the high-voltage battery and circuitry, and the reassembly of the vehicle, all individual assigned duties came into play.
Using proper personal protective equipment (PPE), a student probes an individual battery cell in a high-voltage battery just removed from a 3rd generation Toyota Prius. Credit: NAFTC.
After safe battery removal, each group was assigned the task of probing, documenting, and using Toyota scan tools. To best understand the technology contained in the battery pack, during this information gathering activity, students were asked to illustrate the battery and its components, including voltages measured. By requiring the illustration of the information gained by each group, participants acquired a tactile and lasting knowledge of the construction, components and logic behind the workings of the high-voltage storage system.
This is a sample illustration of a Prius battery pack. Note the voltages listed on each cell and the inclusion of system relays. Credit: NAFTC.
Each battery measurement is discussed in each group and assessments are relayed to the instructor. Proper safety is emphasized and followed at all times, building real-time and future safe practices.
After discussing the finished illustration with the instructor and passing queries from him based on their lab experience, each group was permitted to reinstall the battery back into the vehicle. After reinstallation, a health test was performed using the factory scan tool to assure no diagnostic trouble codes (DTC) were detected.
Students of the recent Electric Drive Vehicle Automotive Technician training are shown reinstalling a battery pack. Credit: NAFTC.
There will be a series of articles highlighting various classroom and shop activities from the Electric Drive Vehicle Automotive Technician training. Next up: Student use of unique tools to evaluate possible issues with battery pack health.
IMPORTANT: Automotive technicians should not attempt to work on electric drive vehicles unless they are properly trained.
NAFTC’s Electric Drive Vehicle Automotive Technician Training
On February 11-15, 2013, the National Alternative Fuels Training Consortium hosted a train-the-trainer class for member training centers on the NAFTC’s brand-new Electric Drive Vehicle Automotive Technician course. This 40-contact hour class combines general and original equipment manufacturer (OEM) specific lessons and skills to safely diagnose, disassemble, and repair electric drive vehicles. The course, which is evenly distributed in both classroom and shop activities, was enthusiastically received by those in attendance. The train-the-trainer course provided a much needed opportunity for schools to incorporate a necessary and desirable skill set in their automotive curricula.
Flexibly designed to be used both as a stand-alone immersion course, or to be distributed throughout a school’s existing coursework through the course’s modular format, all attendees expressed that the information would bring unique and desirable skills to their students.
San Jacinto College in Houston, Texas, a new NAFTC National Training Center member, volunteered to supply the needed shop and classroom space for the training. Their impressive facility was critical for the multiple hands-on and in-depth classroom training that took place. Much of the course training took place in the school’s automotive shop. Multiple electric vehicles were used in the training, including Toyota Prius, Lexus hybrid, Ford C-Max hybrid, and Chevrolet Volt platforms.
A sampling of the hybrid vehicles used in the NAFTC’s Electric Drive Vehicle train-the-trainer course. Credit: NAFTC.
A key portion of the shop work involved training participants on how to safely work with the high-voltage technologies. Many current automotive technicians may be unfamiliar with the differences between low-voltage DC and high-voltage systems, and the course spends extensive time emphasizing safe work practices in dealing with these vehicles.
One of the most liked and informative shop tasks documented in the new course occurred on day four and involved the safe and non-intrusive removal of a hybrid vehicle’s high-voltage battery pack. In using the proper tools, techniques, and proper personal protective equipment (PPE), including high-voltage gloves and leather overgloves, participants were able to incorporate many lessons and technical instructions learned over the course of the training into an intense, yet educational task.
A NAFTC member school instructor begins the process of disconnecting a third generation Prius battery pack in preparation for removal. Credit: NAFTC.
Technicians began the battery pack exercise by removing batteries from electric vehicles. The removal of the battery pack was just the beginning of the whole exercise, however. As a mini-exam, the participants were instructed to map out the battery pack individual modules, high-voltage bus, relays, and other related systems in a rough drafting exercise to fully emphasize their learned knowledge of the battery pack, interlock systems, relays, and voltage transfer systems.
Mapping of the high-voltage battery systems. The removed battery pack can be seen in the background of the photo. Credit: NAFTC.
After completing the week-long event, the NAFTC received the following note from one of the participant’s supervisors on the quality of the course and instruction, and the related excitement it has brought to his department.
Advanced Electric Drive Automotive Technician Training
an Automotive Instructor’s Report
by Wesley Mickens, Chicago Vocational High School
It is Monday morning and I just received a report from one of my instructors who just attended the Electric Drive Vehicle Automotive Technician train-the-trainer in LaPorte, Texas. I was very anxious to hear about his training experience as our school is a new member of the NAFTC and we would like to offer this training in the Chicago area.
The instructor provided me with a written trip report and stated that this training was one of the best he has attended. He started by describing a “powering up” exercise with the Toyota smart keys to demonstrate how the different generations of Toyota hybrid electric vehicles (HEVs) have slight differences in their starting procedures. He then described a detailed exercise using the Toyota Techstream, a PC-based scan tool. (He also submitted a cost analysis to support the purchase of a computer and the Toyota Techstream software for use with our classes in addition to his written report.)
I listened closely as he continued to provide details of the Electric Drive Vehicle Automotive Technician class, including the use of a Pico Scope to scope devices such as System Maintenance Relays (SMR).
He indicated that the highlight of the class for him was removing the HEV battery pack. In fact, he was so excited about this exercise that he provided pictures of the battery pack in his report; see them below.
Credit: Wesley Mickens, Chicago Vocational High School.
His report also indicated that the training participants were shown how to activate inspection mode on Toyota hybrid electric vehicles, and how to place the vehicle in neutral. He also described using the graphing of PIDS on the scan tool, all of which are important procedures when servicing Toyota HEVs.
It’s now 9:05 a.m. and my instructor is needed in class. He left saying that if I want to know more about the class that I should read his written report and then take the class when it’s offered at our school. After seeing his enthusiasm for the course and reading his written report, I will say that am very impressed with the level of training that my instructor received. This course is one that should not be missed.
Chicago Vocational High School
The NAFTC is very proud to offer such a well-received, and in many ways, groundbreaking training course to our member schools. The skill set that the Electric Drive Vehicle Automotive Technician Training program can bring to students definitely give them knowledge and abilities that will give them distinct advantages over other job applicants in the competitive field of automotive repair.
Be sure to watch for future editions of the NAFTC eNews, as over the next few months, the Let’s Clear the Air column will focus on various shop activities conducted during the Electric Drive Vehicle Automotive Technician Training.
This course is being offered as an end-user course at the NAFTC’s national headquarters in Morgantown, WV on March 11-15 and May 20-24, 2013. A second train-the-trainer session for NAFTC members is set for April 15-19, 2013. Further details and registration information can be seen on the NAFTC web site at http://naftc.wvu.edu/
By Mark Schmidt, NAFTC.
In previous “Let’s Clear the Air” articles in this series, we primarily discussed full hybrid technologies and their evolutions, specifically the efforts of Toyota and their Prius program. This article will focus on Honda Motor Company’s early efforts in the hybrid technology field.
Honda’s hybrid beginnings were different from Toyota’s. Honda developed a mild hybrid rather than a full hybrid layout. The company’s first vehicle, released in 1999, was the Honda Insight, which boasted what Honda called an “Integrated Motor Assist” system, or IMA. The IMA system used multiple hardware devices and computers to manage control of the hybrid and conventional technologies, developing the first mass produced mild hybrid of the modern era. It is important to note that Honda used this technology for more than 14 years; the Honda Insight used IMA, or a mild hybrid system, for vehicle propulsion through 2007. Steady improvements were introduced each new model year and built upon to create today’s Honda offerings. The photos and captions below apply specifically to the Honda Insight drive train and systems, from 1999 to 2007.
Intelligent Power Unit
Pictured below is what Honda calls the Intelligent Power Unit, or IPU. One major difference between Honda’s mild hybrid technology and full hybrid technology discussed in earlier eNews articles lies in how the power inverter is cooled. Honda’s system, unlike the liquid cooling used by other manufacturers, uses a simpler air cooling method to cool the inverter.
Photo 1: Intelligent Power Unit (IPU). Source: NAFTC
Notice the two cooling fans in Photo 1. The left fan cools the power inverter, what Honda calls their Motor Drive Module (MDM), while the fan on the right cools the high-voltage battery. The air enters the battery box from a vent located in the passenger compartment. The left fan also cools the DC to DC converter.
Photo 2: Labeled IPU Component Locations. Source: NAFTC
1. Battery Module
2. Junction Board
3. Battery Condition Monitor Module (BCM)
4. Motor Control Module (MCM)
5. Motor Drive Module (MDM)
6. DC-DC Converter
7. Heat Sink (helps to cool the Power Control Unit)
8. Battery Module Cooling Fan
9. MDM/DC-DC Converter Cooling Fan
Note: Components #5, 6, and 7 are known collectively as the Power Control Unit (PCU).
Photo 3: Power Control Unit. Source: NAFTC
5. Motor Drive Module (MDM)
6. DC-DC Converter
7. Heat Sink (helps to cool the Power Control Unit)
The Battery Module
The Battery Module, which contains, among other components, the vehicle’s high voltage battery, is used to supply power to the IMA motor during mild hybrid assist mode. The Battery Module is also used to store regenerated power created when the vehicle is in cruising, deceleration and braking modes.
Specifications on the Battery Module are:
Panasonic nickel metal hydride (NiHM) battery with a rated capacity of 6.5 Ah
Battery is constructed in a modular form and has a terminal voltage of 144V
120 batteries, each battery 1.2 volt, connected in series (120 times 1.2 volts = 144 volts)
Photo 4: The Battery Module.Source: NAFTC
Photo 5: Junction Board. Source: NAFTC
The Junction Board, a component of the Battery Module, is located in the IPU compartment and is attached directly to the Battery Module. When the ignition switch is turned on, two components on the Junction Board operate to allow the electric start-up sequence. The Bypass Contactor (see Photo 5) closes first, followed by the High Voltage Contactor. Note that the Junction Board itself is not a serviceable item.
The Battery Condition Module
The Battery Control Module (BCM) monitors battery temperature and voltage and reports its information to the Motor Control Module (MCM).
The Motor Drive Module
The Integrated Motor Assist system assists the internal combustion engine (ICE) with an electric motor using power from the Battery Module. It must also recharge the Battery Module by using power generated by the electric motor/generator through regenerative braking. It is the Motor Drive Module (MDM), through its bi-directional control, that sends current from the electric motor/generator to the battery, and from the battery to the electric motor (MG), based on need.
During assist mode, power from the Battery Module is supplied to the IMA motor in the form of 3-phase Alternating Current (AC). The current isn’t true AC; however, the Insolated-Gate Bipolar Transistors (IGBT) in the Motor Power Inverter Module are switched in such a way as to simulate an Alternating Current (AC) wave form that produces AC current within the stator of the electric motor or MG.
The Motor Control Module receives constant feedback from three commutation sensors in the IMA Motor and therefore knows the position of the motor. Accurate position information is crucial, as each phase of the 3-phase current must be switched on at the correct time to insure proper motor operation.
The Voltage Converter Module (internal within the MDM) receives commands from the Motor Control Module and switches the IGBTs appropriately to meet system demands.
During regeneration mode, current flows from the IMA motor/generator to the MDM. The electric motor/generator generates true 3-phase Alternating Current, and that AC must be transformed into DC before it can be used to charge the Battery Module. Diodes inside the Motor Power Inverter Module are used to rectify the AC power in the same way as they are used in a typical alternator.
DC to DC Converter
The DC to DC Converter serves the same purpose as a conventional alternator. However, it is a solid state component with no moving parts. Power is supplied to the DC-DC Converter through the MDM or by the Ni-MH Battery Module. This power is reduced to 12 volts to charge the vehicle’s 12V battery and to support the conventional 12V electrical system. It transforms 144V DC as an input source into 12V DC output power.
The 144V Direct Current supplied from the IMA motor or Battery Module is first converted into high voltage Alternating Current, which is then stepped down by a transformer to low voltage AC before being converted back to DC for use by the insight’s 12V electrical system.
The DC-DC converter is a high voltage component and produces substantial heat during operation. To ensure proper cooling of the DC-DC Converter, it is mounted to a finned aluminum heat sink fitted inside a magnesium housing. The Programmed Fuel Injection (PGM-FI) Electronic Control Module (ECM) controls the output of the DC-DC Converter according to power consumption of the 12V electrical system.
IMA Electric Motor/Generator (MG)
In Photo 6, the motor’s rotor mounting is shown, as it is bolted to the engine’s crankshaft. System IMA electronics are responsible for creating the rotating electronic magnetic field in the stator. The rotor has permanent magnets that oppose the stator’s magnetic field.
Photo 6: Motor Generator (MG). Source: NAFTC
The MG’s stator has permanent magnets bolted to the engine crank shaft, as seen in Photo 6. The Motor Control Module (MCM) commands the engine to spin at 1000 revolutions per second. This is the ICE’s primary starter on the vehicle.
The stator’s magnetic field is computer generated and will attract the magnetic rotor. The MG is a 10KW or 13 hp engine.
The engine’s conventional 12 volt starter is used as a back-up for extremely hot or cold temperatures. The 12 volt starter also acted as a fail-safe mode for IMA problems.
The systems illustrated in this article served as the Honda Insight Hybrid system from 1999 to 2007. It was Honda’s gateway technology for what was used in the Honda Civic Hybrid, model year 2003, and is used in Honda’s current model year of hybrid vehicles.
Alternative fuels have been around for decades, but have been increasing in popularity as energy security, the economy, and consumer awareness continue to grow. The goal of this article is to “clear the air” on the topic of energy content. Most concerned citizens may not necessarily be concerned directly with fuels’ energy content. Instead, they may be concerned about vehicle driving range and operating costs, which are most often associated with the total at the pump. However, energy content is an essential component of automotive study. Energy content was recently discussed at the Clean Cities Learning Program’s Petroleum Reduction Technologies regional pilot training in Charleston, WV.
Energy content is the amount of chemical energy contained in a certain amount of a fuel. Most often, the energy content is represented by energy per unit mass. Examples include Btu/lb, kJ/kg, and others. However, it is also important to understand that energy content may be represented on a volume basis such as Btu/gallon or kJ/gallon. Yes, units are often mixed.
Kilojoules or 1,000 joules
British thermal unit
Kilogram or 1,000 grams
Pounds of force per square inch
Kilowatts or 1,000 watts
Miles per gallon
Miles per gasoline gallon equivalent
Fuel economy of alternative fuels
Gasoline gallon equivalent
Equivalent energy content
For anyone that may not know the exact definition of kJ or Btu, check out the following definitions:
A kJ is a kilojoule or 1,000 joules. This is the energy required to raise the temperature of 239 grams of water by 1 °C.
Btu is a British thermal unit. This is the energy required to raise the temperature of one pound of water by 1 °F.
To convert a Btu to kJ, multiply by 1.055. To convert a kJ to Btu, multiply by 0.948.
To convert from lbs to kg, multiply by 0.454. To convert kg to lbs, multiply by 2.2.
This article will look at the energy content of six alternative fuels in comparison with conventional ‘gasoline’ and ‘diesel’. However, both gasoline and diesel have variations in energy content based on blends. Most gasoline sold in the U.S. may have up to 10% ethanol by volume. Pump diesel fuel may also contain a small concentration of biodiesel, usually a few percent. The values presented here are for ‘pure’ gasoline and diesel.
Note: The energy contents presented here are based on the Lower Heating Value (LHV) for each fuel. The density of diesel is approximately 7.15 lbs/gallon. The density of gasoline was taken to be 6.3 lbs/gallon. The density of biodiesel was taken to be 7.34 lbs/gallon. The density of propane was taken to be 4.2 lbs/gallon in the liquid state at 60 °F. The density of hydrogen was taken to be 0.084 kg/cubic meter at 68 °F and ambient pressure. An average density for natural gas was taken to be 0.75 kg/cubic meter at 68 °F at ambient pressure. The density of E85 was taken to be 6.5 lbs/gallon.
E85+ (83% ethanol)
Propane (Liquefied Petroleum Gas, LPG)
Depends on source (coal, natural gas)
So from the Table 1 above we can create Figures 1 and 2. Figure 1 compares the energy content of the fuels by mass, while Figure 2 compares the energy content by volume.
Figure 1: Energy Content by Mass
Figure 2: Energy Content by Volume
As is seen from Figure 2, the energy content by gallon varies significantly between gaseous and liquid fuels. The propane in Figure 2 is a liquid; this is usually accomplished by low pressure tanks. The tank pressures are typically on the order of a few hundred pounds of force per square inch (psi). The pressures of diesel, gasoline, biodiesel, and ethanol are ambient pressures, as these fuels do not require onboard pressurization. The largest disparity is for natural gas and hydrogen, which are shown at near ambient temperatures and pressures. Natural gas is typically stored 3,600 psi in order to increase its volumetric energy density. This allows for a more comparable vehicle range compared to liquid fuels. Hydrogen is usually stored onboard at pressures of at least 5,000 psi to increase its volumetric energy density.
The different fuels have various energy contents by mass and volume. These fuels are stored at various pressures and typically have varying prices. In order to better make a fair comparison between fuels, you may run across the term gasoline gallon equivalent (GGE). Table 2 lists each fuel and how many equivalent units of its fuel yields the energy content in 1 gallon of conventional gasoline.
But for natural gas and hydrogen, how much volume will it take to hold 1 GGE? For hydrogen at 5,000 psi and near ambient temperatures, it will take a volume of about 9.3 gallons to have the same energy as a volume of 1 gallon of gasoline. For natural gas at 3,600 psi and near ambient temperatures, it will take a volume of about 3.5 gallons to have the same energy as a volume of 1 gallon of gasoline.
GGEs of alternative fuels are handy for a few reasons. One, they can help to better compare the prices of the fuels based on energy content instead of units purchased. Two, they can help to explain why vehicles may travel different ranges when switching fuels. For the second reason, we will introduce the miles per gasoline gallon equivalent (MPGe) measurement.
For the first reason, we can walk through an example on how to estimate the GGE cost of electricity to charge our new battery electric vehicle (BEV). If we were to purchase a gallon of gasoline, we would expect to pay an average price of $3.85 this week. If you look at your electric bill, you may find that you are currently paying an average price of $0.12 per kW-hr. To find out the price of a GGE of electricity, multiply 33.70 kW-hr/GGE by $0.12/kW-hr. This yields a GGE price of about $4.04. So in this case, electricity would cost about $0.19 more per GGE than gasoline. This may make many people shudder and say, why would we switch to a BEV? Well, remember, if we were ‘filling up’ our Nissan Leaf as an example, we would be getting a fuel economy of up to 106 MPGe in the city. That’s 3-4 times higher than most conventional vehicles. This example shows where the savings may occur.
This understanding of energy can also help when understanding battery size and BEV range. Let’s stick with the Leaf as an example. Instead of having a gas tank with a volume like conventional vehicles, it has a battery with a capacity. The capacity of batteries is usually measured in kW-hr. The Leaf’s lithium ion battery is rated at 24 kW-hr. We know that a GGE of electricity is about 33.70 kW-hr. So if the math is correct, that means that a Nissan Leaf only has about the equivalent onboard energy as about 0.71 gallons of gasoline. It seems really low. But again, the fuel economy of this vehicle can be as high as 106 MPGe. Let’s multiply 106 by 0.71 and see what we get. Well, that number would be about 75.26 miles. If you look at Nissan’s website, they advertise a range of up to 73 miles. This number is slightly lower because of combined highway and city MPGe estimates.
Now that we have touched on MPGe again in example one, let’s look at the second reason why everyone should understand GGE. This relates to the driving range of an alternative fueled vehicle. Let’s say you just purchased a new 2012 flexible fuel sport utility vehicle. When filling up on conventional gasoline, you were only getting about 22 miles per gallon, conventional MPG. However, you spot an E85 refueling station and decide to fill up your empty tank on ethanol. If the blend is around 83% ethanol, your driving range will decrease. If your FFV has a tank volume of 25 gallons you were previously able to drive about 550 miles. However, it takes 1.3 gallons of E85 to yield the same energy as 1 gallon of gasoline from the above GGE table. Since the energy content decreased but the fuel tank stayed the same size, you can estimate that you will only be able to drive around 420 miles or get about 17 MPG. So, why would a customer want to run E85 when there is a decrease in fuel economy and range? Well, remember that it has lower energy content by volume so the vehicle is not running any less efficiently or poorly. In fact, research may soon yield FFVs that are able to improve fuel economy when running on higher blends of ethanol. So if you decide to fill up on E85, don’t be alarmed if your ‘MPG’ drops. The MPGe should stay about the same. Remember from above+ that E85 can be a blend of anywhere from 51-83% ethanol, so real world values may vary if you do not know which blend you actually purchase.
Hopefully, this article has shed some light on GGE and MPGe. Both of these terms are being seen more and more with the increasing numbers of available alternative fuel vehicles. It is better to have a basic understanding of these differences in order to understand how and why these various vehicles perform differently based on fuel type.
CNG Use Ramping Up and NAFTC CNG Materials Getting Revamped
By Derek Johnson
Natural gas is a domestically produced alternative fuel. It has the potential to produce fewer emissions and save money while providing the same performance in vehicles as conventional gasoline and diesel fuels. The amount of proven natural gas reserves continues to grow as new drilling and well technologies are recovering more natural gas from domestic wells. The natural gas boom in the U.S. is leading to the rebirth of the compressed natural gas (CNG) vehicle industry. Manufacturers and conversion companies are keeping up with demand by ramping up production of CNG vehicles.
Taking notice of the CNG boom, the National Alternative Fuels Training Consortium (NAFTC) is focusing on updating its Light-Duty CNG Vehicles and CNG Vehicle Fuel System Inspector curricula. The Light-Duty CNG Vehicles manual will cover everything from basic introductory natural gas information to specific technical discussions of CNG vehicle components and operation. The manual will also include new information on current CNG conversion systems. Many CNG vehicles are converted gasoline vehicles and this is an important area of the market where more knowledge and understanding is needed. This new portion will also allow for more hands-on learning in a laboratory/shop environment.
The CNG Vehicle Fuel System Inspector manual will cover not only the introductory material but also the technical information required for inspection of CNG vehicle fuel systems. In the manual, component design and installation follow various government and association guidelines. In addition, the manual will include details on visual inspection of a CNG system based on current industry standards. The inspector course will serve as a valuable tool in providing participants with a solid foundation, which is required to pass current industry certification exams.
As the number of CNG vehicles increase, there will be a bigger demand for employees with a fundamental knowledge and awareness of CNG vehicles and their operation. In addition, there will be an increased demand in qualified inspectors to insure the proper and safe installation and use of these vehicles.
During the week of October 8-12, 2012, the NAFTC took a proactive approach by having an internal curricula review. The meeting was organized by NAFTC Curriculum and Training Director, Micheal Smyth. Two internal NAFTC reviewers, including myself (Derek Johnson PhD. Mechanical Engineering, Instructional Designer) and Mark Schmidt, National Instructor, participated in the week long review and brainstorming session. In order to better align the materials with industry practice and new technologies, the NAFTC also brought in two external Subject Matter Experts (SMEs). The SMEs were Nick Wagoner and Arthur Holbert. Wagoner is an industry expert in CNG vehicle conversion installations and President of Fuel Conversion Solutions LLC1, based in Grain Valley, Missouri. Holbert is an industry expert in implementation and design of the conversion systems and is the Product Development Manager at NatGasCar LLC2, located in Cleveland, Ohio. NatGasCar LLC provides (EPA and CARB3) certified systems for a variety of Chrysler Group and Volkswagen vehicles.
With these two SMEs, the entire process from system design and certification to conversion of end-user vehicles was covered. The rewriting and editing process is currently underway. New manual design, layout, the latest advances in technology information, and high quality images were discussed and will be implemented to produce brand new manuals for both courses.
In addition to the brainstorming and review process, NAFTC employees were able to view and drive one of NatGasCar’s development vehicles, which were featured in the January 2012 edition of Popular Mechanics. Figures 1 and 2 show the converted van in one of the NAFTC garage bays while it was fueling from the NAFTC’s time-fill CNG station. To read more about this vehicle, read the entire Popular Mechanics article here.
Figure 1: Type 4 composite CNG cylinder installed in rear of converted van. Source: NAFTC.
Figure 2: CNG fill valve connected to NAFTC time-fill CNG station. Source: NAFTC.
It is clear that the natural gas industry is booming across the U.S. and conversion and installation companies are busy modifying vehicles to run on domestic natural gas. The NAFTC is excited to produce peer-reviewed education and training materials and help spread awareness of alternative fuels and advanced technology vehicles. The updated curricula should be available in early 2013. For more information on NAFTC curricula and courses please contact – Micheal Smyth, Assistant Director Training and Curriculum Development, at Micheal.Smyth@mail.wvu.edu or at 304-293-7882.1 http://fuelconversionsolutions.com/fcs/
By Mark Schmidt, NAFTC.
This is the third article in a series describing the evolution of hybrid electric vehicles in this country part one, part two. This article will cover the components that were not used or were modified from the first generation Prius and components in part one of the series of articles.
Push button start (new)
Electronic park switch (new)
Electronic parking lock actuator (new)
Selector lever (new)
Smart key (new)
Electric Air Conditioning called Cooler Compressor / or Electric Inverter Compressor (New)
The second generation Prius added a push button start, electronic park switch, electronic parking lock actuator, selector lever, smart key, an electric AC compressor, a re-designed inverter with Voltage Boosting, and a redesigned power steering system. All these systems were not a part of the 1st generation Prius. Let’s examine each of these new components.
The High Voltage Battery in the 2nd generation is smaller and lighter due to the fact that 10 less battery modules are used compared to the first generation. Its 28 modules produce 201.6 volts direct current (DC). The reduced voltage of the 2nd generation Prius is possible because of the use of a voltage boosting inverter.
The Power Button (see Photo 1) functions the same as the ignition key in a conventional vehicle. If the driver presses the power button once with the brake pedal applied, the instrument display lights up. The Prius hybrid system is now awake and ready to accept additional requests from the driver, such as forward or reverse motion, air conditioning, and other features of a ‘running’ vehicle. As a safety feature, the driver may shut down the system at any time by pressing and holding the power button for 3 seconds even if the vehicle is in motion. This function is the same as turning off a conventional vehicle’s ignition key, which can also be switched off while the vehicle is moving. When the vehicle is at rest with no vehicle speed, the power button may be monetary pressed and the hybrid system will shut down.
Photo 1: Toyota Prius Power Button. Credit: NAFTC
The Park Position Switch is operated by the driver of the vehicle to engage the electronic park function of the transmission. When the selection is made to engage the Park function an indicator light will be illuminated on the top of the switch. Rather than a traditional transmission lever, the parking function is activated by pressing a button (see Photo 2). Push it once, the light is illuminated showing that the vehicle is in park. Now engaged, the transmission locks the drivetrain so that the vehicle’s front wheels cannot rotate. Unlock occurs when the shift lever selection is made requesting forward, reverse or the B position.
Photo 2: The park switch. Credit: NAFTC
This hybrid system judges the vehicle conditions based on the information from various sensors, switches, and electronic control units (ECUs) and activates appropriate shift control in accordance with the driver’s selection. Figure 1 illustrates the vehicles shift lever, parking button, and the ECUs that process requests and relay information between the vehicle subsystems.
Figure 1: Shift and Park Selection System. Credit: NAFTC
Selector Lever Assembly / Shift Lever Position Sensor has four positions
The P Position Switch reports its request to the hybrid vehicle electronic control unit (HV ECU), if conditions are correct for park. The hybrid vehicle ECU then commands the transmission control ECU to actuate the parking lock actuator mounted on the transmission. Unlock occurs if conditions are correct as determined by the HV ECU. This occurs when the shift lever position sensor reports a forward, reverse, or braking request from the driver.
When the driver selects a shift lever position, the corresponding hybrid vehicle’s computer notes the drivers request and caries out the action. The action may require the internal combustion engine (ICE) and/or the hybrid transaxle to carry out the request. The HV ECU processes the request and commands the inverter to apply three phase current to the cables for motor-generator 2 (MG 2). MG 2 will propel the vehicle in a forward or reverse direction depending on the selection. If it is necessary to operate the ICE, the inverter is commanded to operate motor-generator 1 (MG 1) to start the ICE. The gasoline engine may work with MG 2 in all forward positions to assist in forward propulsion.
When the braking (B) position is selected by the shift lever the HV ECU commands the inverter to apply a current to MG 2 that is used to create a magnetic brake through the use of planetary gears to link the drivetrain to the ICE. This is different than regenerative braking. The B position is selected when the driver is descending down a long steep grade and the high voltage battery is charged to full capacity.
The Smart Key
The smart key (see Photo 3) and related electronic modules enables the driver of the vehicle to place the smart key in a pocket or purse, and approach the vehicle as though it were unlocked. As the smart key makes an electrical handshake with the vehicle and the driver torches the driver’s door handle, the door lock unlocks. The electrical handshake that allowed the driver to enter the vehicle also prepares the vehicle for identification by thief deterrent system.
Photo 3: Smart key. Credit: NAFTC
Cooler Compressor/Electric Inverter Compressor
The vehicle’s inverter supplies 201.6 volts direct current to the cooler compressor/electric inverter compressor to rotate the compressor (see Photo 4). The system operates on the same principle as conventional air conditioner systems but uses a special lubricant and is not belt driven. This stand-alone cooling system is necessary to ensure that cabin cooling is available when the vehicle is in operation without the ICE running. This would not be possible when the ICE is off and the accessory belt does not rotate.
Photo 4: Cooler Compressor/Electric Inverter Compressor. Credit: NAFTC
The redesigned inverter receives 201.6 volts direct current from the high voltage battery via the orange high voltage cables (see Photo 5). The DC energy is converted to alternating current (AC) and sent to both MG 1 and MG 2 residing in the hybrid transaxle. Motor speed, horsepower (HP) and torque are controlled by the inverter. When braking, the hybrid transaxles generates electricity from MG 2 and the inverter reverses the sequence and converts AC to DC and sends it back to the HV battery for charging.
The major difference with the re-designed inverter other than appearance is the boost capabilities. The 201.6 volts DC is stepped up by the inverter to as much as 650 volts DC before the conversion is made to AC. The horsepower of the MG’s is directly proportional to the voltage they receive. The higher the voltage sent to the MG, the higher the output HP. The boost transformer is internal to the inverter and is controlled by the HV ECU.
Photo 5: Third generation Toyota Prius inverter. Credit: NAFTC
In summary, the second and third generations have evolved Toyota’s hybrid technology paving the way for new models in Toyota’s Prius hybrid fleet, including the Prius Plug-In, Prius C, and Prius V. After the success of the first generation Prius, Toyota was able to focus on system optimization to improve on the overall efficiency of its Hybrid Synergy system while reducing cost. Now with various Prius and other model options, individuals not only have the choice between conventional and hybrid vehicles but the choice of what hybrid model best suits their driving needs.
By Mark Schmidt, NAFTC
This article is part two in a series describing the evolution of hybrid electric vehicles in this country. Part one can be found here. This article will cover unique characteristics of the Toyota Prius, including its Atkinson Cycle internal combustion engine (ICE).
The Toyota Prius gasoline engine is equipped with special components that allow for its operation on the Atkinson Cycle, which complements the hybrid electric drive powertrain. This engine is an inline 4-cylinder, 1.5-liters, 16-valve Dual Over Head Camshafts (DOHC) engine that is designed to operate over a high-expansion ratio Atkinson Cycle. This engine technology is used in all three generations of Prius gasoline engines. Operation on the Atkinson Cycle is made possible by Toyota’s VVT-i (Variable Valve Timing-intelligent) system. This system is also used in conjunction with ETCS-i (Electric Throttle Control System-intelligent) and an exhaust gas recirculation (EGR) system employing a highly efficient EGR cooler. In addition, use of an electric water pump, power steering pump and AC compressor has eliminated the need for a V-ribbed belt. Thus, improved engine performance, quietness, fuel economy, and cleaner emissions have been achieved.
I feel the need to make a statement before we continue. As we examine the workings of the Atkinson Cycle design, we will examine when the intake valve closes and how this concept relates to reducing pumping losses. The key to understanding the Atkinson Cycle is to focus on what differentiates it from conventional engine valve technology, as only full hybrid technology is able to take full advantage of the Atkinson Cycle design.
The valve timing specifications illustrated in Figure 1 are for the second generation Prius (2004-2009). The first generation Prius (2001-2003) works under the same concept; however the range of valve opening and closing is slightly different. Notice the range of possible times that the intake valves may close in relationship to crankshaft degrees of rotation: 61° after bottom dead center (ABDC) to 102° ABDC. Considering the fact that the piston is traveling upward during the compression stroke in the range listed above, a comparison may be made between non-Atkinson (conventional non-hybrid application) and a hybrid vehicle.
Figure 1 Atkinson Cycle Valve Timing. Credit: Toyota
29° BTDC to 12° ATDC
61° ABDC to 102° ABDC
In most non-hybrid engine powered vehicles, the intake valve is closed much sooner, or closer to bottom dead center (BDC) just after the fuel is injected. As a result, the air fuel mixture will begin compression as the piston is traveling upward, utilizing the long sweep of the compression stroke.
What is different about an Atkinson engine is that the intake valve may be closed very late into the compression stroke 102° ABDC.
The advantage of leaving the intake valve open as the piston travels upward is that the compression area now includes the intake manifold plus the combustion area. This enlarged pressurization area will reduce pumping losses, discussed below. Just before the intake valve closes, the fuel is injected. From this point forward, the air fuel ratio is compressed and the spark plug ignites the air fuel mixture as normal. Conventional engines have a slight advantage over Atkinson Cycle engines with respect to low end torque; however, the torque of electric motors in hybrid vehicle mates well with this operation. For non-hybrid vehicles, turbocharging or supercharging may be used in conjunction with variable valve timing and direct injection to increase engine torque and efficiency. The use of variable valve timing on both the intake and exhaust valve camshafts is becoming more common in many vehicles.
What are pumping losses?
What advantage is there to pumping air from the combustion chamber into the intake manifold? The answer is that positive pressure helps prevent pumping losses, which reduces wasted work. Under certain conditions, the throttle plate creates a negative pressure (vacuum) on the top of the pistons. As the pistons travel downward, resistance created by vacuum tries to slow their motion. That resistance is the negative pressure on the top of the pistons. The pressure pumped into the intake helps equalize the pressure so it is closer to the same pressure on both sides of the throttle plate, thus reducing pumping losses.
Below in Figures 2 and 3, the components of the Atkinson Cycle valvetrain are displayed.
Figure 2 Atkinson Cycle valve train. Credit: Toyota
No. 2 Chain Vibration Damper
No. 1 Chain Vibration Damper
Roller Rocker Arm
Figure 3 Atkinson Cycle camshafts. Credit: Toyota
Oil Passage (Advance)
Oil Passage (Retard)
In part three of this series, we will examine the changes between the first generation Prius and subsequent models.
New Vehicles, More Acronyms
By Derek Johnson, NAFTC
One solution to increase fuel economy in light-duty vehicles has been to use diesel engines, which are known for their fuel economy. They are also known, however, for their emissions.
The EPA introduced new stringent standards for particulate matter (PM) and oxides of nitrogen (NOx) in 2007. They were phased in over a three-year period until full compliance in 2010. While diesel engine use in passenger cars has been limited in the U.S., the technology is common in trucks. New technologies are allowing for both fuel economy benefits and cleaner exhaust from diesel engines. These engines may penetrate into the light-duty vehicle sector as the technology evolves.
These advanced technology engines are now two to five years old. As warranties expire and mileage accumulates, there will be inevitable maintenance and systems failures related to emissions control systems .
Coming from an engineering background at West Virginia University’s Center for Alternative Fuels, Engines, and Emissions (CAFEE), I am familiar with the mindset of engineers in the field: use more acronyms. It will prove beneficial to be aware of the meaning behind these acronyms. Their use will become more prevalent as these vehicles begin to see time in maintenance garages. The following systems focused on increased performance while reducing two main emissions:
NOx – Oxides of nitrogen, typically NO with some NO2. These are regulated emissions from all engines and are formed when nitrogen reacts with oxygen at high pressures and temperatures. NOx has both negative environmental and health effects. Three-way catalysts (TWCs) are used in stoichiometric gasoline engines to reduce NOx emissions. These emissions are difficult to eliminate in the lean (oxygen rich) exhaust of diesel vehicles.
PM – Particulate matter. This may be best described by the black smoke emitted from older diesel engines. It is made of many compounds that may include, but are not limited to, oxides of sulfur formations, unburned diesel fuel, elemental carbon compounds and ash.
The following list pertains to technologies that have been developed to help reduce the emissions from advanced diesel engines.
ULSD – Ultra-low sulfur diesel. This fuel has a maximum sulfur content of 15 parts per million (ppm) compared to previous levels of 500 ppm. The reduction of sulfur content has reduced oxides of sulfur (SOx) emissions; however, its use is required with advanced exhaust aftertreatment systems. Use of high sulfur fuels with these systems causes catalyst poisoning with sulphate compounds that can render the aftertreatment system useless.
EGR – Exhaust gas recirculation. This has been applied to gasoline engines for years but has gained prominence with diesel engines within the past decade. These systems are often liquid cooled and electronically controlled. Some of the exhaust gas is cooled and then flows into the engine intake to decrease combustion temperatures, in turn lowering NOx emissions. Some systems have been known to have problems with failure to do PM loading.
VGT – Variable geometry turbocharging. Turbocharging allows for increased efficiency and performance by boosting the air pressure entering the engine. It also leads to high in-cylinder temperatures and NOx emissions. Electronic controls have been implemented to allow for both controlled performance and emissions reductions by advanced turbocharging systems.
DOC – Diesel oxidation catalysts. These devices were some of the first exhaust aftertreatment systems applied to diesel exhausts. They are used to reduce emissions of unburned fuel, hydrocarbons (HCs), carbon monoxide (CO) and some PM (usually around 25 percent). They are also used to change the makeup of NOx emissions for use with other exhaust aftertreatment systems.
Example of DOC mounted in-line with vehicle exhaust system. DOC circled. Source: CAFEE.
DPF – Diesel particulate filter. These devices are used in order to meet PM reduction requirements. Now standard components of diesel exhaust systems, they are typically ceramic, honeycomb type bricks that have alternating passages blocked off. The exhaust flows through the filter wall. The larger PM particles are trapped inside. This PM builds up over time and must be oxidized (burned) into the main by-product of carbon dioxide (CO2). Some designs only require operation of the vehicle under certain loads for what is termed regeneration. Under these conditions, there is sufficient heat and NO2 available to oxidize the filtered PM. Most systems are equipped with temperature and pressure sensors in trigger active regeneration. When there is an active regeneration, either the engine fuel injectors or secondary injector add fuel to the exhaust. The added fuel combusts within the filter and cleans out the filtered PM. These systems do add backpressure and fuel economy penalties to engine performance. Many new vehicles may have lights on the instrument cluster that depict if a regeneration event is required or underway, as well as if there are DPF problems. Diesel vehicles equipped with DPFs will not emit plumes of black smoke that are associated with diesel engines.
DPF equipped truck being emissions tested by CAFEE. DPF circled. Source: CAFEE.
LNT – Lean NOx Trap. While DPFs are able to reduce PM, other systems are needed to reduce NOx. LNTs work on the principle of adsorbing NOx species during the common lean burn operation of diesel engines. To reduce the stored NOx into nitrogen (N2), there are typically rich-burn engine events that release and reduce the stored NOx. A version of this system is used in Volkswagen TDI (Turbocharged Direct Injection) vehicles.
SCR – Selective catalytic reduction. This is currently the leading and most applied NOx reduction system to meet 2010 NOx requirements. This system uses special catalyst materials along with the injection of urea to reduce NOx to N2. The urea is an added liquid that is stored on board in a separate tank. It is commonly advertised to consumers as diesel exhaust fluid (DEF). It is injected into the hot exhaust, where it decomposes to form ammonia (NH3). The ammonia reacts with the NOx within the catalyst and reduces to nitrogen. There are also instrument cluster lights indicating malfunctioning SCR systems and urea level indicators. If the systems are used without urea, the light will illuminate and may cause the vehicle to operate in a “limp-home” mode until the issue is addressed. Each vehicle manufacturer has different types of limp-home modes. When vehicles are in limp-home mode, they often have reduced power and speed but are still able to move. This is so the engine or aftertreatment systems are not damaged. Its inconvenience ensures that the problem is remedied quickly.
Many 2010 diesel-powered vehicles combine EGR, ULSD, VGTs, DOCs, DPFs and SCR or LNT systems. These systems require monitoring of added temperature, pressure and NOx sensors. They also control fuel or urea injection. Actuators on turbochargers and EGR valves are used for additional control. These new integrated systems often require an added onboard electronic control unit (ECU). Malfunctioning systems will display Society of Automotive Engineers (SAE) J1939 parameter identifications (PIDs). Simple diesel engines are a thing of the past, and new advanced systems continue to evolve. New diesel engines will require additional maintenance and troubleshooting of emissions control components. Vehicles with these technologies have accumulated miles and may be out of warranty. Therefore, service technicians and vehicle owners will be pushed into a world filled with simple acronyms for complex systems.
As a “CNG person,” I have watched compressed natural gas (CNG) system integrity and operation over an extended period of time with interest.. In the area where I live, many vehicles are driven until they die. The truck I drive is a 1999 with 310,000 miles, my work car has 227,000 miles, and our minivan had more than 350,000 miles when our college-age daughter bought her own vehicle, so we sold it.
During a recent engine performance class for beginning CNG technicians, our discussion turned to system degradation over time. We brought in two older CNG dual-fuel vehicles that have racked up a lot of miles. The following is a brief description of what we found. First off, let me share how we ran some of the tests. We used a chassis dynamometer that enabled us to operate the vehicle at a steady speed and then apply a load to the vehicle. This was done for the same vehicles operating on gasoline and CNG in order to compare their respective emissions.
Using three different five gas analyzers, we verified the emissions results. The five gas analyzer sample lines were placed in the vehicles tailpipe exit (see Figure 1). These analyzers measured emissions of hydrocarbons (HC), carbon monoxide (CO), carbon dioxide (CO2), oxygen (O2), and oxides of nitrogen (NOx).
The first vehicle was a 1998 model year with 184,000 miles. The check engine light was off, and there were no codes in the computer. During our pre-stress inspection, we found numerous vacuum leaks with a smoke machine the spark plugs had been changed only once! The plug we pulled had .065 inch gap and was worn out. The air filter was dirty and very little maintenance had ever been done on this vehicle. We ran the vehicle at 50 miles per hour (mph) with a 10 percent load in fourth gear.
The measured concentrations were high when the vehicle was operated on gasoline. When operated on gasoline the exhaust gas concentration of HC was 650 parts per million (ppm) while the CO2 concentration was just over 7percent. When we switched the vehicle to natural gas, the HC concentration went up to more than 1,100 PPM and CO2 was more than 9 percent.
The second vehicle tested was a 1993 truck with 135,000 miles. This truck had been well maintained with new filters, regular maintenance, and a little care. Don’t get me wrong, this is a three-fourths-ton work vehicle that is used fairly hard, but along with the use, it receives regular maintenance.
The test conditions of the second vehicle can be seen in the screen shot of Figure 2. The tested vehicle speed was 48 mph, with a 20 percent load. The engine torque and horsepower were 225 lb ft and 68 hp, respectively.
The exhaust gas concentrations of HC, CO, CO2 and O2 are shown in Figure 3 as the vehicle operated on gasoline. The concentrations for this 19-year-old work truck were surprisingly low.
Next we changed the fuel to CNG and ran the test again at the same operating points. There were less than two minutes between the two tests. The exhaust gas concentrations of HC, CO, CO2 and O2 are shown in Figure 4 as the vehicle operated on natural gas. It is seen that HC and CO emissions were lower while running on natural gas while O2 and CO2 concentrations were higher.I find that with CNG, maintenance is key.
NG has a higher firing KV (voltage required by the spark plug to ignite the fuel), which will accentuate any secondary problems. We have seen numerous customer concerns in which the vehicle seems to run properly on gasoline, but they notice a performance problem while operating on natural gas. This maintenance issue can be seen by comparing the concentrations of the harmful and regulated emissions of HC and CO for the vehicle operating on gasoline and natural gas.
Our job as technicians is to provide quality maintenance on alternative fuel vehicles in order to maintain the integrity of the system. As demonstrated by the first vehicle, emissions are higher and drivability problems are accentuated when maintenance is neglected on CNG vehicles.
Disclaimer Stan Martineau is an ASE Master Auto, Truck, Advanced specialist, Alternative Fuel CNG specialist at Utah State University/College of Eastern Utah, an NAFTC National Training Center. Martineau is the guest commentator for this column. His content and opinions do not necessarily reflect that of the NAFTC.