Search Results

A prior study (Chon and Heywood, [1]) examined how the design and performance of spark-ignition engines evolved in the United States during the 1980s and 1990s. This paper carries out a similar analysis of trends in basic engine design and performance characteristics over the past decade. Available databases on engine specifications in the U.S., Europe, and Japan were used as the sources of information. Parameters analyzed were maximum torque, power, and speed; number of cylinders and engine configuration, cylinder displacement, bore, stroke, compression ratio; valvetrain configuration, number of valves and their control; port or direct fuel injection; naturally-aspirated or turbocharged engine concepts; spark-ignition and diesel engines. Design features are correlated with these engine’s performance parameters, normalized by engine and cylinder displacement.

An experimental study was performed to develop a more fundamental understanding of the effects of secondary air injection (SAI) on exhaust gas emissions and catalyst light-off characteristics during cold start of a modern SI engine. The effects of engine operating parameters and various secondary air injection strategies such as spark retardation, fuel enrichment, secondary air injection location and air flow rate were investigated to understand the mixing, heat loss, and thermal and catalytic oxidation processes associated with SAI. Time-resolved HC, CO and CO₂ concentrations were tracked from the cylinder exit to the catalytic converter outlet and converted to time-resolved mass emissions by applying an instantaneous exhaust mass flow rate model. A phenomenological model of exhaust heat transfer combined with the gas composition analysis was also developed to define the thermal and chemical energy state of the exhaust gas with SAI.

Mechanisms of NH₃ generation using LNT-like catalysts have been studied in a bench reactor over a wide range of temperatures, flow rates, reformer catalyst types and synthetic exhaust-gas compositions. The experiments showed that the on board production of sufficient quantities of ammonia on board for SCR operation appeared feasible, and the results identified the range of conditions for the efficient generation of ammonia. In addition, the effects of reformer catalysts using the water-gas-shift reaction as an in-situ source of the required hydrogen for the reactions are also illustrated. Computations of the NH₃ and NOx kinetics have also been carried out and are presented. Design and impregnation of the SCR catalyst in proximity to the ammonia source is the next logical step. A heated synthetic-exhaust gas flow bench was used for the experiments under carefully controlled simulated exhaust compositions.

The challenge posed by the long run times necessary to accurately quantify ash effects on diesel aftertreatment systems has led to numerous efforts to artificially accelerate ash loading, with varying degrees of success. In this study, a heavy-duty diesel engine was outfitted with a specially designed rapid lubricant degradation and aftertreatment ash loading system. Unlike previous attempts, the proposed methodology utilizes a series of thermal reactors and combustors to simulate all three major oil consumption mechanisms, namely combustion in the power cylinder, evaporative and volatile losses, and liquid losses through the valve and turbocharger seals. In order to simulate these processes, each thermal reactor allows for the precise control of the level of lubricant additive degradation, as well as the form and quantity of degradation products introduced into the exhaust upstream of the aftertreatment system.

An experimental study was conducted on a spark-ignited direct-injection engine burning fuels with different evaporation and autoignition characteristics. The test engine was a single-cylinder Direct-Injection Stratified-Charge (DISC) engine incorporating a combustion process similar to the Texaco Controlled Combustion System. Two fuels were tested and compared with a baseline gasoline fuel: diesel fuel, and gasoline mixed with an ignition improver. The tests were done at low to medium engine loads. Diesel fuel was found to have similar levels of hydrocarbon (HC) emissions as gasoline but had different characteristics. The optimum timing for diesel fuel was retarded from that for gasoline and combustion variability was much less with diesel than with gasoline. Gasoline with a commercial ignition improver normally used to increase the cetane number of diesel fuel was also tested. The effect of changing the autoignition quality of the fuel depended on the injector used.

Light-load unburned hydrocarbon emissions were studied experimentally in a spark-ignited direct-injection engine burning gasoline where the piston temperature was varied. The test engine was a single-cylinder Direct Injection Stratified-Charge (DISC) engine incorporating a combustion process similar to the Texaco Controlled Combustion System. At a single low load operating condition, the piston temperature was varied by 50 K by controlling the cooling water and oil temperature. The effect of this change on unburned hydrocarbon emissions and heat release profiles was studied. It was found that by carefully controlling the intake air temperature and pressure to maintain constant in-cylinder conditions at the time of injection, the change in piston temperature did not have a significant effect on the unburned hydrocarbon emissions from the engine.

In order to understand better the operation of spark-ignition engines during the warm-up period, a computer model had been developed which simulates the thermal processes of the engine. This model is based on lumped thermal capacitance methods for the major engine components, as well as the exhaust system. Coolant and oil flows, and their respective heat transfer rates are modeled, as well as friction heat generation relations. Piston-liner heat transfer is calculated based on a thermal resistance method, which includes the effects of piston and ring material and design, oil film thickness, and piston-liner crevice. Piston/liner crevice changes are calculated based on thermal expansion rates and are used in conjunction with a crevice-region unburned hydrocarbon model to predict the contribution to emissions from this source.

Parallel measurements of lubricant-film behavior and oil consumption in two identical small production IDI diesel engines are presented. Oil consumption was measured using tritium as a radioactive tracer, and instantaneous film thickness data between the piston and liner were obtained using laser fluorescence diagnostics. The data covered single- and multi-grade lubricants and five different ring configurations (two-piece vs three-piece rings at various ring tensions). The data illustrate (a) oil-film profiles under the rings, especially around the leading and trailing edges, (b) accumulation of oil on piston lands and skirt, (c) circumferential variations around the bore, (d) observations on ring rotation, and (e) the piston-skirt oil-pumping mechanism. Effects of lubricants and piston-ring configurations on oil-film characteristics are investigated, and the oil consumption data are compared with oil-film thickness measurements.

While metal fiber filters have successfully shown a high degree of particle retention functionality for various sizes of diesel engines with a low pressure drop and a relatively high filtration efficiency, little is known about the effects of lubricant-derived ash on the fiber filter systems. Sintered metal fiber filters (SMF-DPF), when used downstream from a diesel engine, effectively trap and oxidize diesel particulate matter via an electrically heated regeneration process where a specific voltage and current are applied to the sintered alloy fibers. In this manner the filter media essentially acts as a resistive heater to generate temperatures high enough to oxidize the carbonaceous particulate matter, which is typically in excess of 600°C.

In the study of internal combustion engines, gas temperatures within the system are of significant importance. The adverse conditions under firing operation, however, make measurements by any means very difficult. This current study seems to have gone the farthest to date for velocity of sound gas temperature measurements in internal combustion engine applications. An ultrasound signal is sent by a transmitting transducer, through the gas medium, and into the receiving transducer. The received signal is recorded, and the gas temperature determined from the time of flight. In-cylinder and exhaust manifold gas temperatures under fired conditions are presented, and are all consistent. Impacts of operating parameters like mixture equivalence ratio and coolant temperature are investigated.

A dynamometer-mounted four-cylinder Saturn engine was used to accumulate combustion chamber deposits (CCD), using an additized fuel. During each deposit accumulation test, the HC emissions were continuously measured. The deposit thickness at the center of the piston was measured at the beginning of each day. After the 50 and 35-hour tests, HC emissions were measured with isooctane, benzene, toluene, and xylene, with the deposited engine, and again after the deposits had been cleaned from the engine. The HC emissions showed a rapid rise in the first 10 to 15 hours and stabilization after about 25 hours of deposit accumulation. The HC increase due to CCD accumulation accounted for 10 to 20% of the total engine-out HC emissions from the deposit build-up fuel and 10 to 30% from benzene, isooctane, toluene, and xylene, making CCDs a significant HC emissions source from this engine. The HC emissions stabilized long before the deposit thickness.

Previous research has shown the potential benefits of running an engine with excess air. The challenges of running lean have also been identified, but not all of them have been fundamentally explained. Under high dilution levels, a lean limit is reached where combustion becomes unstable, significantly deteriorating drivability and engine efficiency, thus limiting the full potential of lean combustion. This paper expands the understanding of lean combustion by explaining the fundamentals behind this rapid rise in combustion variability and how this instability can be reduced. A flame entrainment combustion model was used to explain the fundamentals behind the observed combustion behavior in a comprehensive set of lean gasoline and hydrogen-enhanced cylinder pressure data in an SI engine. The data covered a wide range of operating conditions including different compression ratios, loads, types of dilution, fuels including levels of hydrogen enhancement, and levels of turbulence.

In this study, changes in the composition of lubricant additives in the power cylinder oil are examined. Samples are extracted from a single cylinder heavy-duty diesel engine in two locations during engine operation; the crankcase and the top ring groove of the piston. Emissions of lubricant-derived ash-forming elements are lower than would be expected based on oil consumption and crankcase oil composition. This occurs partly because the inorganic additive compounds are less volatile than light-end hydrocarbons in the base oil. The tribology of the piston ring pack also affects the composition of the oil consumed in the power cylinder system. The elemental composition of oil extracted from the top ring groove is significantly different than the crankcase oil. Additive metals are concentrated in the top ring groove of the power cylinder. Detergent compounds (i.e. Ca and Mg) concentrate due to the volatility of the base oil. The metals associated with ZDDP (i.e.

For some time, spatial nonuniformities in the unburned mixture within a spark ignition engine have been suspected of contributing to cycle-by-cycle variations in combustion. In this work, an experimental structure was developed that allowed the effects of fuel/air nonuniformity and residual gas/fresh charge nonuniformity to be separately addressed, with special regard given to their impact on the flame development process and combustion rate. Under the conditions of light loads and low speed, it was found that a decrease in fuel-air nonuniformity caused a slight reduction in the variation of the early flame development angle but had no significant impact on the statistics of the main combustion phase or IMEP. Eliminating residual gas nonuniformity by skip firing the engine and adding equivalent residual to the fresh mixture prior to entry to the cylinder had no detectable impact on the flame development process.

The effects of injection variability, low velocity fuel injection, and injector orifice size on unburned hydrocarbon emissions were studied in a direct-injection stratified-charge (DISC) engine. The engine incorporated a combustion process similar to the Texaco Controlled Combustion System (TCCS) and was operated with gasoline. The variability in the amount of fuel injected per cycle was found to have a negligible effect on HC emissions. Changing the amount of fuel injected at low velocity at the end of injection impacted the HC emissions by up to 50%. A positive pressure differential between the injection line and the combustion chamber when the injector needle closed resulted in more fuel injected at low velocity and increased HC emissions. High speed single frame photography was used to observe the end of injection. Injectors with smaller orifices had substantially lower HC emissions than the baseline injector.

Experiments were carried out to collect in-cylinder pressure data and microphone signals from a single-cylinder test engine using spark timingsbefore, at, and after knock onset for toluene reference fuels. The objective was to gain insight into the phenomena that determine knock onset, detected by an external microphone. In particular, the study examines how the end-gas autoignition process changes as the engine's spark timing is advanced through the borderline knock limit into the engine's knocking regime. Fast Fourier transforms (FFT) and bandpass filtering techniques were used to process the recorded cylinder pressure data to determine knock intensities for each cycle. Two characteristic pressure oscillation frequencies were detected: a peak just above 6 kHz and a range of peaks in the 15-22 kHz range. The microphone data shows that the audible knock signal has the same 6 kHz peak.

The life of an automotive engine is often limited by the ability of its components to resist wear. Zinc dialkyldithiophosphate (ZDDP) is an engine oil additive that reduces wear in an engine by forming solid antiwear films at points of moving contact. The effects of this additive are fairly well understood, but there is little theory behind the kinetics of antiwear film formation and removal. This lack of dynamic modeling makes it difficult to predict the effects of wear at the design stage for an engine component or a lubricant formulation. The purpose of this discussion is to develop a framework for modeling the formation and evolution of ZDDP antiwear films based on the relevant chemical pathways and physical mechanisms at work.

Liquid fuel flow into the cylinder an important source of hydrocarbon (HC) emissions of an SI engine. This is an especially important HC source during engine warm up. This paper examines the phenomena that determine the inflow of liquid fuel through the intake valve during a simulated start-up procedure. A Phase Doppler Particle Analyzer (PDPA) was used to measure the size and velocity of liquid fuel droplets in the vicinity of the intake valve in a firing transparent flow-visualization engine. These characteristics were measured as a function of engine running time and crank angle position during four stroke cycle. Droplet characteristics were measured at 7 angular positions in 5 planes around the circumference of the intake valve for both open and closed-valve injection. Additionally the cone shaped geometry of the entering liquid fuel spray was visualized using a Planar Laser Induced Fluorescence (PLIF) setup on the same engine.

This paper is a direct continuation of a previous study that addressed the performance and design of a variable compression engine, the Alvar-Cycle Engine [1]. The earlier study was presented at the SAE International Conference and Exposition in Detroit during February 23-26, 1998 as SAE paper 981027. In the present paper test results from a single cylinder prototype are reviewed and compared with a similar conventional engine. Efficiency and emissions are shown as function of speed, load, and compression ratio. The influence of residual gas on knock characteristics is shown. The potential for high power density through heavy supercharging is analyzed.

The oil control ring is the most critical component for oil consumption and friction from the piston system in internal combustion engines. Three-piece oil control rings are widely used in Spark Ignition (SI) engines. However, the dynamics and lubrication of three piece oil control rings have not been thoroughly studied from the theoretical point of view. In this work, a model was developed to predict side sealing, bore sealing, friction, and asperity contact between rails and groove as well as between rails and the liner in a Three Piece Oil Control Ring (TPOCR). The model couples the axial and twist dynamics of the two rails of TPOCR and the lubrication between two rails and the cylinder bore. Detailed rail/groove and rail/liner interactions were considered. The pressure distribution from oil squeezing and asperity contact between the flanks of the rails and the groove were both considered for rail/groove interaction.