DIAGNOSTIC TROUBLE CODE DEFINITIONS

<div class="section abstract"> <div class="htmlview paragraph">This SAE Recommended Practice is applicable to all E/E systems on MD and HD vehicles. The terms defined are largely focused on compression-ignited and spark-ignited engines. Specific applications of this document include diagnostic, service and repair manuals, bulletins and updates, training manuals, repair data bases, under-hood emission labels, and emission certification applications.</div> <div class="htmlview paragraph">This document focuses on diagnostic terms, definitions, abbreviations, and acronyms applicable to E/E systems. It also covers mechanical systems which require definition.</div> <div class="htmlview paragraph">Nothing in this document should be construed as prohibiting the introduction of a term, abbreviation, or acronym not covered by this document. The use and appropriate updating of this document is strongly encouraged.</div> <div class="htmlview paragraph">Certain terms have already been in common use and are readily understood by manufacturers and technicians, but do not follow the methodology of this document. To preserve this understanding, these terms were included and have been identified with the footnote (2), "historically acceptable common usage," so they will not erroneously serve as a precedent in the construction of new names. These terms fall into three categories:</div> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">a</span> <div class="htmlview paragraph">Acronyms that do not logically fit the term.</div></li> <li class="list-item"> <span class="li-label">b</span> <div class="htmlview paragraph">Acronyms existing at the component level, i.e., their terms contain the base word or noun that describes the generic item that is being further defined.</div></li> <li class="list-item"> <span class="li-label">c</span> <div class="htmlview paragraph">Acronyms for terms that appear to contain the base word, but are frequently used as a modifier to another base word. (This use may possibly be thought of as following the methodology since the acronym is normally used as a modifier.)</div></li></ol></div>

<div class="htmlview paragraph">The ongoing advances being made in electronics technology has made it possible to expand the range of microcomputer applications in automotive engine control systems. Progress in this field of application has given rise to very sophisticated control systems called total engine control systems, which are designed to provide interacting control with other subsystems (e.g., antiskid braking system, traction control system, transmission control system), instead of just controlling the engine itself. Improved engine control system performance and more versatile functions have made the application software controlling the system larger, with more complex control processing.</div> <div class="htmlview paragraph">Until now, control processing in engine control systems could be implemented by the microcomputer's interrupt processing program alone. However, because engine control systems have grown in both size and complexity, it has become difficult to determine the sequence in which processing programs (tasks) are to be executed. Consequently, the basic software (realtime operating system) that efficiently makes this determination has become necessary.</div> <div class="htmlview paragraph">This paper describes the use of microcomputers in engine control systems by using our newly developed μPD78602 16-Bit Single-Chip Microcomputer that incorporates a realtime operating system as firmware (alias Realtime Task Manager: RTM) as an example.</div>

<div class="section abstract"><div class="htmlview paragraph">Automatic transmission (AT) is a complex hydroelectromechanical system, since it consists of hydraulic, electrical and mechanical parts.</div><div class="htmlview paragraph">On cars produced by “UzAuto Motors” mainly AT of the 6T family, 6-speed AT family GM: 6T30, 6T40, 6T45, 6T50 “Hydra-Matic” are used.</div><div class="htmlview paragraph">Production of parts of these transmissions is carried out both at American GM plants and at GM plants in China and Korea.</div><div class="htmlview paragraph">The differences between AT 6T30/6T40/6T45/6T50 are in the thickness of the output chain and in the planetary gear, in the sizes of some other units and the housing itself. But the differences are much more influenced by the settings of the transmission unit, which select operating modes with different engines so as not to overload the thinnest places of the automatic transmission.</div><div class="htmlview paragraph">Automatic transmissions 6T30, 6T40, 6T45, 6T50 have the ability to manually shift gears and activate the “kickdown” mode (for quick acceleration of the car, when you sharply press the gas “all the way” it makes the automatic transmission downshift, and sometimes by two steps).</div><div class="htmlview paragraph">The operation of the transmission is controlled by various electronic systems that are responsible for the operability and structural integrity of the gearbox.</div><div class="htmlview paragraph">Failure of the automatic transmission can occur as a result of one or a combination of malfunctions of the following parts: in the torque converter; in the mechanical part of the gearbox; in the hydraulic part of the control system; one or more clutches of the gearbox; in the electrical part of the control system; in the electronic control unit.</div><div class="htmlview paragraph">The authors of the work investigated and determined the occurrence of malfunctions and failures depending on the temperature of the working fluid of the automatic transmission of a passenger car.</div><div class="htmlview paragraph">Also, the dependence of the resource of the automatic transmission on the temperature of the hydraulic fluid was obtained. High-quality diagnostics of the automatic transmission and its control system can in many cases save the car owner from expensive repairs: <ul class="list disc"><li class="list-item"><div class="htmlview paragraph">without thorough diagnostics, the automatic transmission cannot be subjected to routine or major repairs. Only on the basis of diagnostic information can a conclusion be made about the technical maintenance or repair of the automatic transmission;</div></li><li class="list-item"><div class="htmlview paragraph">based on real experience of operating passenger cars equipped with automatic transmission, we recommend changing the oil every 35000 miles under operating conditions in Tashkent. We also recommend conducting diagnostics of the automatic transmission every 12500 miles of the car's mileage.</div></li></ul></div></div>

<div class="htmlview paragraph">Advances in integrated circuit technology over the past few years have led to the development of a group of technologies that have been classed as smart power. These new technologies now allow the semiconductor manufacturer to include logic and analog control on the same monolithic device with power transistors capable of controlling many Watts of output power. Recently developed devices have the capability to control up to 400 Watts of power delivered to the load with a single monolithic integrated circuit.</div> <div class="htmlview paragraph">Many of the Smart Power technologies are compatible with the automotive environment and may be used to fabricate devices for power actuation in an automotive multiplex control system. This paper gives a brief overview of four smart power technologies and their applications in an automotive multiplex control system for body electric. Two specific devices recently developed in these technologies are introduced.</div>

<div class="htmlview paragraph">This paper describes the development process for acceleration sensors used on automobiles and acceleration evaluation system especially for the acceleration in super low range frequency.</div> <div class="htmlview paragraph">Acceleration sensor is indispensable not only for good vehicle motion control system, for example, active suspension control system, antiskid control system and four wheel steering control system, but also for safety system like air bag control system. This work focused on the development process of acceleration sensor which applied piezo ceramics.</div> <div class="htmlview paragraph">Features of newly developed sensor are as follows.</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"> <span class="li-label">1)</span> <div class="htmlview paragraph">Achievement of self-diagnostic function to detect sensor failure utilizing the characteristics of piezo ceramics</div> </li> <li class="list-item"> <span class="li-label">2)</span> <div class="htmlview paragraph">Addition of piezo ceramic to cancel the pyro-effect achieved stabilization of sensor characteristics and enabled to detect acceleration of 0.0025G in super low range frequency of 0.05Hz.</div> </li> <li class="list-item"> <span class="li-label">3)</span> <div class="htmlview paragraph">Incorporates impedance conversion, filtering and temperature characteristics compensation circuitry.</div> </li> </ol> </div> <div class="htmlview paragraph">Frequency range of acceleration for good vehicle motion control is considered to be from DC to about 50Hz.</div> <div class="htmlview paragraph">But the measurement of acceleration in thus super low range frequency near DC had been difficult because of its mechanical and electrical noise interruption.</div> <div class="htmlview paragraph">This had delayed the development of acceleration sensor for automotive use.</div> <div class="htmlview paragraph">We succeeded in the development of acceleration measurement system for super low range frequency from 0.01Hz to 2Hz with detecting acceleration range from 0.0002 (0.2 gal) G to 1G as well as the development of piezo type acceleration sensor for automotive use.</div>

<div class="section abstract"> <div class="htmlview paragraph">This Recommended Practice provides a procedure for measuring and documenting the aerodynamic performance in a full-scale wind tunnel of passenger vehicles, i.e., mass-produced cars and light-duty trucks intended primarily for individual consumers. Testing or numerical modeling of pre-production and/or reduced-scale models is outside the scope of this document. Aerodynamic <i>development</i> procedures, i.e., methods to improve or optimize aerodynamic performance, are also excluded.</div> <div class="htmlview paragraph">It is well-known that aerodynamic performance results depend significantly on vehicle content and loading, as well as the wind tunnel itself (type, scale, and simulation qualities of the wind tunnel). Publication of non-standard test results causes unnecessary additional development work and incorrect perception of a vehicle’s anticipated aerodynamic performance by government, academia, and the general public.</div> <div class="htmlview paragraph">The intent of this document is to promote uniformity and traceability of published aerodynamic performance data acquired in a wind tunnel, thereby enhancing the public reputation and credibility of the aerodynamics discipline in the total vehicle development process.</div> <div class="htmlview paragraph">Measurement of the aerodynamic performance according to this Recommended Practice requires a full-scale wind tunnel test on a production-ready, full-scale vehicle according to specifications for vehicle loading, content, and wind tunnel conditions.</div> <div class="htmlview paragraph">The measurement and resulting documentation for a particular vehicle shall be reported only by the company that intends to produce the vehicle. Whenever there is an opportunity for interpretation of the document, a good faith effort shall be made to obtain the vehicle’s typical in-service performance and avoid finding the best possible performance under the best possible circumstances.</div> <div class="htmlview paragraph">Use of and compliance with this Recommended Practice is voluntary; however, it is mandatory for those advertising or otherwise publishing aerodynamic performance as “measured according to SAE J2881.” Conversely, any advertised or otherwise published result carrying this or a substantially similar designation must have the necessary documentation accepted by and on file with the SAE in accordance with the procedures defined in this Recommended Practice.</div> <div class="htmlview paragraph"><span class="xref">Appendices B</span> and <span class="xref">C</span> contain the necessary submittal documents for compliance with this Recommended Practice. When a submittal is made, the chairman of the Road Vehicle Aerodynamics Forum Committee (RVAC) or his/her designee shall review the submittal for proper completion according to the requirements herein, but without consideration of the technical merit of the claimed performance. After the chairman’s review, SAE will maintain an electronic database of all submittals.</div> <div class="htmlview paragraph">The database shall be available only to members and liasion members of the RVAC. Any RVAC member who retrieves information from the database shall do so with the understanding that the information is to be considered confidential within his or her company.</div></div>

<div class="htmlview paragraph">This work is a joint development project between Chrysler and CFD Research Corporation (CFDRC). The objective of this investigation is to perform a 3D computational heat transfer analysis in a vehicle passenger compartment, for better climate control, under external thermal radiation. One of the major tasks is to simulate the transient temperature variation in the passenger compartment after the AC unit is turned on.</div> <div class="htmlview paragraph">Two physical models were incorporated in the computations, namely, the radiation model and the conjugate heat transfer methodology. The 3D radiation model was employed to evaluate the solar irradiation through the glazed surfaces, namely, the front windshield, the rear window, and the two side windows. Conjugate heat transfer methodology was employed to compute the heat transfer across the glazed surfaces due to heat conduction and convection. These developed models were then integrated and incorporated into the CFD-ACE code, a multi-domain, 2D and 3D combined general equation solver developed by CFDRC.</div> <div class="htmlview paragraph">Comparison shows very reasonable agreement between computational results and experimental data obtained from vehicle hot room cool down tests. This study demonstrates that Computational Fluid Dynamics (CFD) technology can be used as a design and prototyping tool for automotive climate control systems.</div>

<div class="htmlview paragraph">The Columbus laboratory module, developed by Astrium Bremen as prime contractor and Alenia Spazio as co-prime, is the European contribution to the International Space Station (ISS) program and as such it will support, once in orbit, micro-gravity and space based research activities of the member states.</div> <div class="htmlview paragraph">Columbus Environmental Control System (ECS) employs an Environmental Control and Life Support System (ECLSS) providing atmosphere pressure, cabin ventilation and temperature humidity control inside the module in conjunction with an autonomous Active Thermal Control System (ATCS) that provides the heat collection capability. The ATCS, based on software controlled water loop, provides also the cooling capability for Payloads and Subsystem equipment. The ECS is completed with the Passive Thermal Control System based on software controlled shell heating system plus passive fixtures such as Multi-Layers Insulation (MLI) blankets.</div> <div class="htmlview paragraph">Generally, both, the Columbus ATCS as well as the ECLSS are qualified via simplified but representative tests and concluding analyses. Complete verification of the module thermal and environmental control design however, will be performed via analysis supported by ECS System Level Integrated Test as well as the predictions for flight.</div> <div class="htmlview paragraph">With respect to responsibility sharing, Alenia is responsible for all verification by test related to thermal/environmental aspects, i.e. Alenia will define the test requirements and cases to be performed via the establishment of a dedicated test specification. On the other side, definition and production of the test set-up as well as the performance of the test is assigned to the Columbus prime Astrium SI Bremen.</div> <div class="htmlview paragraph">In order to get confidence on the functional performance of the Columbus ECS and to validate the Integrated Overall Thermal Mathematical Model (IOTMM) on system level the module will be subjected to an Integrated System Test (IST).</div> <div class="htmlview paragraph">Purpose of the ECS IST is to provide the first verification of the thermal/environmental interrelation between the active cooling (ATCS) and environmental control system (ECLSS) hardware and software and to collect as much characteristic thermal data as possible for the validation of the flight configuration IOTMM. This test will represent the second and last test in series on the flight configuration of the Columbus module.</div> <div class="htmlview paragraph">Previous tests, for verification of the functional interfaces of the ATCS and ECLSS, have been performed already in the frame of the Electrical Test Model (ETM) utilization. However, this test did not provide information on environmental and thermal parameters of the system but rather on the functional interrelations of the relevant units of the subsystems. Presently, the subject test will be performed in the integration hall of Astrium SI Bremen (Class 100.000 clean room conditions) and the pressurized shell is planned to be covered by the flight multi-layer insulation only located beneath the meteoroid debris panels (MDPS) of the module. However, in order to get as much as possible characteristic data of the system not only the test cases have to be selected very carefully but also additional test supporting equipment (TSE) has to be evaluated.</div> <div class="htmlview paragraph">The present paper summarizes the efforts generated to establish the Environmental/Thermal test in the frame of the system level IST of the Columbus module, describes the interrelation aspects of the thermal/environmental subsystem verification by test and analysis and presents the derived methodologies and expected results.</div>

<div class="htmlview paragraph">This article describes a new transmission control system for off-highway dump trucks with small electro-hydraulic control valves which are individually equipped for each clutch. The new system mainly improves shift shocks by generating suitable clutch pressure curves while shifting.</div> <div class="htmlview paragraph">This system has some important technical points.</div> <div class="htmlview paragraph">The first one is the mechanism of the small electro-hydraulic control valve. It has two spools. One spool controls clutch pressure, and another controls oil flow and senses oil pressure. This valve recognizes the moment at which the clutch pack is filled up. It enables us to control not only the pressure curves of clutches, but also the timing of engagement and disengagement of clutches.</div> <div class="htmlview paragraph">Next technical point is that every clutch is equipped with one valve. Since one valve holds the pressure of a clutch which is being disengaged until another clutch, which is controlled by another valve, is filled up, we can keep driving torque while shifting. We developed so called “Torque-continuous shifting”.</div> <div class="htmlview paragraph">The last point is that the clutch pressure is controlled according to driving condition by an electronic control system. Using this system, we can easily get the most suitable clutch pressure for any driving condition. One drawback of using electronic system is that it is a little troublesome for mechanics to repair or to do trouble shooting. To make the repairwork easier, we provided a self diagnosis system, which also memorizes troubles in the past in a non-volatilize random access memory.</div> <div class="htmlview paragraph">This system has been already applied to our off-highway dump trucks since 1988, and has received good reputation.</div>

<div class="htmlview paragraph">The effect of the gasoline antiknock additive, MMT, on automotive emission control systems was studied in a 63-car field test. The cars were operated for 50 000 miles, and the effects of MMT on hydrocarbon, CO and NOx emissions, catalyst plugging and spark plug life were determined.</div> <div class="htmlview paragraph">Two concentration levels of MMT in a clear base fuel were studied, 1/32 g Mn/gal and 1/16 g Mn/gal. Seven 1977-78 model year cars, all calibrated to meet California standards, were included in the statistical design.</div> <div class="htmlview paragraph">The results of this study indicate that the use of MMT at either test concentration increases both engine and tailpipe hydrocarbon emissions, compared to clear fuel. At 50K miles, the average tailpipe hydrocarbon increase was 0.09 g/mile for 1/32 MMT fuel, and 0.11 g/mile for 1/16 MMT fuel. This increase was pronounced at low mileage intervals, and significant differences continued for the duration of the test. CO and NO<sub>x</sub> emissions, catalyst plugging, and spark plug life were not affected by MMT.</div>

<div class="htmlview paragraph">The IC for a CIG-FIP (Chip In Glass Fluorescent Indicator Panel) having functions of keyboard scan and digital/analog brightness control has been developed. The panel has 60 segments, grid pre-driver, function of digital/analog brightness control ( dimming ), and function of scanning 5 x 6 matrix keyboard.</div> <div class="htmlview paragraph">The results of the IC on several evaluation are also described. According to the results, it is confirmed that there are no problems about IC to apply in FIP process.</div> <div class="htmlview paragraph">It will be suitable for automotive climate control system, audio system and so on.</div>

<div class="section abstract"> <div class="htmlview paragraph">This recommended practice aims to establish a common output format of crash-related data recorded and stored within certain electronic components currently installed in many light-duty vehicles. This document pertains only to the post-download format of such data and is not intended to standardize the format of the data stored within any on-board storage unit, or to standardize the method of data recording, storing, or extraction.</div> <div class="htmlview paragraph">Historically, crash data recording technology in light-duty vehicles has developed and evolved based on differing technical needs of manufacturers and their customers without industry standards or government regulation. As a result, wide variations currently exist among vehicle manufacturers regarding the scope and extent of recorded data. This document is intended to be a compilation of data elements that various manufacturers are currently recording, as well as those elements reasonably predicted to be recorded in the foreseeable future, and establishes a common output format of those data elements.</div> <div class="htmlview paragraph">The scope of this document is deliberately restricted to providing output data formatting guidelines, only. It is not intended to standardize or mandate the recording of any specific data elements or to specify a minimum data set. This restriction in the scope is to avoid imposing constraints on the type of data recorded, the method of gathering and storing data, and the pre-and/or post-processing of data that may be used by various vehicle/device manufacturers as a matter of proprietary design. The committee recognized that, given the lack of societal consensus regarding the acceptability of on-board data recording devices, and has therefore avoided specific recommendations concerning whether event data recorders should be equipped on motor vehicles, and whether, when implemented, a particular type, quantity, and manner of data collection should be used.</div> <div class="htmlview paragraph">Readers of this series of documents are advised to examine the validity and accuracy of VEDI event data in conjunction with the results from the traditional accident reconstruction practice. Since VEDI event data are acquired only from the on-board electronics systems, they may have not accurately capture the actual dynamics of the vehicle during the accident, or may not contain the full range or length of data during the event.</div> <div class="htmlview paragraph">This document is one of a multi-volume J1698 series of documents and provides general concepts and common definitions of event data recording. J1698-1 provides definitions of event data and J1698-2 provides data extraction protocols.</div> </div>

<div class="htmlview paragraph">Regulated and non-regulated emissions from five current European diesel passenger cars and one light-duty diesel truck were measured to assess the environmental impact of diesel vehicles and to help determine the emission characteristics of the two types of combustion systems: indirect injection (IDI) and high speed direct injection (HSDI). The vehicle emissions were measured using the European Motor Vehicle Emissions Group (MVEG) cycle and the U.S. Federal (FTP 75) test procedures. Measured emissions included HC, CO, NO<sub>x</sub> and particulate mass (PM), C<sub>1</sub> to C<sub>12</sub> hydrocarbon species (here called light hydrocarbon or LHC), aldehydes, particulate composition and particle size distribution. The particulate composition measurements included soluble organic fraction (SOF), its oil and fuel sub-fractions, and the sulfate fraction. All passenger cars and the light-duty commercial vehicle tested complied with the current European Emissions Directive 91/441/EEC. Two passenger cars achieved the EEC Stage 2 levels, and one nearly met the 1994 Tier I U.S. Federal standards. The LHC accounted for between 35 to 78% of the total HC measured by the heated FID analyzer. Fuel and oil comprised between 12 and 30% of the PM emissions. The non-methane organic gases (NMOG) emissions and the LHC ozone reactivity from diesel cars were both about 50% less than those from gasoline cars. Of the non-regulated emissions, formaldehyde was generally below 0.009 g/km, and benzene emissions were below 0.0035 mg/km. The results were compared with European gasoline vehicles and the Current Gasoline Vehicle fleet of the U.S. Air Quality Improvement Program (AQIRP), and an assessment was made of the relative environmental impacts of gasoline and diesel vehicles.</div> <div class="htmlview paragraph">Over the last 20 years, there has been a substantial effort to lower the exhaust emissions from both diesel and gasoline passenger vehicles. Over the same period, the percentage of diesel passenger vehicles purchased in Europe has been increasing steadily(<span class="xref">1</span>)<span class="xref">*</span>. Lower operating(<span class="xref">2</span>) and maintenance costs, and better durability with equivalent drive performance appear mainly responsible for the increased diesel sales. However, even though both diesel and gasoline vehicles meet the current emission standards, questions have arisen about their relative impact on the environment(<span class="xref">3</span>). In addition, with future requirements for lower emissions, these questions will undoubtedly continue.</div> <div class="htmlview paragraph">The relative environmental impact of diesel and gasoline vehicles is still uncertain because there are relatively few published data on the emissions of current diesel vehicles and because the environmental impacts of the expected emissions are not clearly understood. Data on the regulated emissions for diesel passenger vehicles sold in Europe are available from the German Government:(<span class="xref">4</span>) starting in 1991. There are also published reports on regulated emissions from late 1980 and early 1990 diesel cars in the literature(<span class="xref">5</span>,<span class="xref">6</span>,<span class="xref">7</span>). Still there are few reports on the non-regulated emissions from current diesel vehicles(<span class="xref">8</span>,<span class="xref">9</span>,<span class="xref">10</span>).</div> <div class="htmlview paragraph">On the other hand, there are substantial published data on the regulated emissions of current gasoline vehicles(<span class="xref">11</span>). In addition, there are substantial data on the non-regulated emissions of gasoline cars, especially from the U.S. Air Quality Improvement Research Program (AQIRP)(<span class="xref">12</span>). The AQIRP emissions data included measurements of over 150 individual hydrocarbon and aldehydic compounds which allow estimates of the amount of urban ozone formed from the exhaust and of the atmospheric toxic compound levels. Diesel vehicles were not included in AQIRP.</div> <div class="htmlview paragraph">This paper reports on detail regulated and non-regulated emissions measurements for six 1992/93 model year diesel vehicles, including two Ford and four competitor vehicles. The emissions were measured on both the 1993 European MVEG cycle and the U. S. Federal test procedure. The U. S. AQIRP analytical methods were used for hydrocarbon and aldehydic speciation. The report discusses the regulated emissions from the six diesel vehicles compared to emissions standards, their contribution to urban ozone formation, toxic levels and global warming. It also compares the exhaust emissions of current diesel and gasoline vehicles to help clarify their relative environmental impact.</div>

<div class="htmlview paragraph">A recently introduced 3 Digit Monolithic A/D Converter makes highly reliable automotive data acquisition and control systems easy to design and fabricate. The device includes many significant performance features, requires a minimum of external components and provides the outstanding stability and reliability needed for automotive control and instrumentation systems. This I.C., the LD130 offers an extremely accurate (0.1%) conversion from an analog input to a Binary-Coded-Decimal (BCD) output, an easily handled output format for interfacing both displays and microprocessors.</div>

<div class="section abstract"><div class="htmlview paragraph">Two modern light-duty passenger vehicles were selected for chassis dynamometer testing to evaluate differences in performance end efficiency resulting from CNG and gasoline combustion in a vehicle-based context. The vehicles were chosen to be as similar as possible apart from fuel type, sharing similar test weights and identical driveline configurations.</div><div class="htmlview paragraph">Both vehicles were tested over several chassis dynamometer driving cycles, where it was found that the CNG vehicle exhibited 3-9% lower fuel economy than the gasoline-fueled subject. Performance tests were also conducted, where the CNG vehicle's lower tractive effort capability and longer acceleration times were consistent with the lower rated torque and power of its engine as compared to the gasoline model.</div><div class="htmlview paragraph">The vehicles were also tested using quasi-steady-state chassis dynamometer techniques, wherein a series of engine operating points were studied. When the indicated thermal efficiency at each point was calculated, it was found that the CNG vehicle typically exhibited lower thermal efficiency.</div><div class="htmlview paragraph">Several operating points were chosen for further characterization of engine efficiency and combustion behavior, including an analysis of losses. Though the CNG engine had better theoretical efficiency potential, the losses suffered by this engine were repeatedly more significant than those suffered by the gasoline engine. As a result, the CNG engine was typically less efficient. There were a number of factors contributing to this phenomenon, including compression ratio, fuel properties, ignition and combustion timing and phasing, as well as EGR rates.</div></div>