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Difficulties in the starting and operation of diesel engines at low temperatures are an important consideration in their design and operation, and in selection of the fuels for their use. Improvements in operation have been achieved primarily through external components of the engine and associated subsystems. A Rapid Compression Machine (RCM) has been modified to operate over a wide range of temperatures (−20°C to 100°C). It is used to isolate the combustion chamber in an environment in which all significant parameters are carefully defined and monitored. The influence of temperature and cetane number on the ignition and combustion processes are analyzed. Examination of the combustion characteristics show that temperature is by far the most influential factor affecting both ignition delay and heat release profiles. Cetane number (ASTM D-613) is not found to be a strong indicator of ignition delay for the conditions investigated.

A spark-ignition engine friction model developed by Patton et al. in the late 1980s was evaluated against current engine friction data, and improved. The model, which was based on a combination of fundamental scaling laws and empirical results, includes predictions of rubbing losses from the crankshaft, reciprocating, and valvetrain components, auxiliary losses from engine accessories, and pumping losses from the intake and exhaust systems. These predictions were based on engine friction data collected between 1980 and 1988. Some of the terms are derived from lubrication theory. Other terms were derived empirically from measurements of individual friction components from engine teardown experiments. Recent engine developments (e.g., improved oils, surface finish on piston liners, valve train mechanisms) suggested that the model needed updating.

A set of experiments was performed to investigate the effects of relative air-fuel ratio, inlet boost pressure, and compression ratio on engine knock behavior. Selected operating conditions were also examined with simulated hydrogen rich fuel reformate added to the gasoline-air intake mixture. For each operating condition knock limited spark advance was found for a range of octane numbers (ON) for two fuel types: primary reference fuels (PRFs), and toluene reference fuels (TRFs). A smaller set of experiments was also performed with unleaded test gasolines. A combustion phasing parameter based on the timing of 50% mass fraction burned, termed “combustion retard”, was used as it correlates well to engine performance. The combustion retard required to just avoid knock increases with relative air-fuel ratio for PRFs and decreases with air-fuel ratio for TRFs.

Engine oil consumption is recognized to be a significant source of pollutant emissions. Unburned or partially burned oil in the exhaust gases contributes directly to hydrocarbon and particulate emissions. In addition, chemical compounds present in oil additives poison catalytic converters and reduce their conversion efficiency. Oil consumption can increase significantly during critical non-steady operating conditions. This study analyzes the oil consumption behavior during ramp transients in load by combining oil consumption measurements, in-cylinder measurements, and computer-based modeling. A sulfur based oil consumption method was used to measure real-time oil consumption during ramp transients in load at constant speed in a production spark ignition engine. Additionally in-cylinder liquid oil behavior along the piston was studied using a one-point Laser-Induced-Fluorescence (LIF) technique.

As part of ongoing research on hydrogen-enhanced lean burn SI engines, this paper details an experimental combustion system optimization program. Experiments focused on three key areas: the ignition system, in-cylinder charge motion produced by changes in the inlet ports, and uniformity of fuel-air mixture preparation. Hydrogen enhancement is obtained with a H2, CO, N2 mixture produced by a fuel reformer such as the plasmatron. The ignition system tests compared a standard inductive coil scheme against high-energy discharge systems. Charge motion experiments focused on the impact of different flow and turbulence patterns generated within the cylinder by restrictor plates at the intake port entrance, as well as novel inlet flow modification cones. The in-cylinder fluid motion generated by each configuration was characterized using swirl and tumble flow benches. Mixture preparation tests compared a standard single-hole pintle port fuel injector against a fine atomizing 12-hole injector.

This paper reviews the major changes that have occurred in spark-ignition engine design and operation over the last two decades. The automobile air pollution problem, automobile emission standards, and automobile fuel economy standards -- the factors which have and are producing these changes -- are briefly described. The major components in spark-ignition engine emission control systems are outlined, and advances in carburetion, fuel injection, ignition systems, spark retard and exhaust gas recycle strategies, and catalytic converters, are reviewed. The impact of these emission controls on vehicle fuel economy is assessed. The potential for fuel economy improvements in conventional spark-ignition engines is examined, and promising developments in improved engine and vehicle matching are outlined.

An experimental study was performed to investigate the effects of various intake charge motion control valves (CMCVs) on mixture preparation, combustion, and hydrocarbon (HC) emissions during the cold start-up process of a port fuel injected spark ignition (SI) engine. Different charge motions were produced by three differently shaped plates in the CMCV device, each of which blocked off 75% of the engine's intake ports. Time-resolved HC, CO and CO2 concentrations were measured at the exhaust port exit in order to achieve cycle-by-cycle engine-out HC mass and in-cylinder air/fuel ratio. Combustion characteristics were examined through a thermodynamic burn rate analysis. Cold-fluid steady state experiments were carried out with the CMCV open and closed. Enhanced charge motion with the CMCV closed was found to shorten the combustion duration, which caused the location of 50% mass fraction burned (MFB) to occur up to 5° CA earlier for the same spark timing.

In an effort to both increase engine efficiency and generate new, consistent, and reliable data useful for the development of engine concepts, a modern single-cylinder 4-valve spark-ignition research engine was used to determine the response of indicated engine efficiency to combustion phasing, relative air-fuel ratio, compression ratio, and load. Combustion modeling was then used to help explain the observed trends, and the limitations on achieving higher efficiency. This paper analyzes the logic behind such gains in efficiency and presents correlations of the experimental data. The results are helpful for examining the potential for more efficient engine designs, where high compression ratios can be used under lean or dilute regimes, at a variety of loads.

Dilute operation of a SI engine offers attractive performance incentives. Lowered combustion temperatures and changes in the mixture composition inhibit NOx formation and increase the effective value of the ratio of burned gas specific heats, increasing gross indicated efficiency. Additionally, reduced intake manifold throttling minimizes pumping losses, leading to higher net indicated efficiency. These benefits are offset by the reduced combustion speed of dilute fuel-air mixtures, which can lead to high cycle-to-cycle variation and unacceptable engine behavior characteristics. Hydrogen enhancement can suppress the undesirable consequences of dilute operation by accelerating the combustion process, thereby extending the dilution limit. Hydrogen would be produced on-board the vehicle with a gasoline reforming device such as the plasmatron. High dilution at higher loads would necessitate boosting to meet the appropriate engine specific power requirements.

Experiments to study the effects of oxygenated fuels on emissions and combustion were performed in a single-cylinder direct-injection (DI) diesel engine. A matrix of oxygen containing fuels assessed the impact of weight percent oxygen content, oxygenate chemical structure, and oxygenate volatility on emissions. Several oxygenated chemicals were blended with an ultra-low sulfur diesel fuel and evaluated at an equivalent energy release and combustion phasing. Additional experiments investigated the effectiveness of oxygenated fuels at a different engine load, a matched fuel/air equivalence ratio, and blended with a diesel fuel from the Fischer-Tropsch process. Interactions between emissions and critical engine operating parameters were also quantified. A scanning mobility particle sizer (SMPS) was used to evaluate particle size distributions, in addition to particulate matter (PM) filter and oxides of nitrogen (NOx) measurements.

Experiments were conducted to determine the effects of substantial spark retard on combustion, hydrocarbon (HC) emissions, and exhaust temperature, under cold engine conditions. A single-cylinder research engine was operated at 20° C fluid temperatures for various spark timings and relative air/fuel ratios. Combustion stability was observed to decrease as the phasing of the 50% mass fraction burned (MFB) occurred later in the expansion stroke. A thermodynamic burn rate analysis indicated combustion was complete at exhaust valve opening with -20° before top dead center (BTDC) spark timings. Chemical and thermal energy of the exhaust gas was tracked from cylinder-exit to the exhaust runner. Time-resolved HC concentrations measured in the port and runner were mass weighted to obtain an exhaust HC mass flow rate. Results were compared to time averaged well downstream HC levels.

The flow into and out of the piston top-land crevice of a spark-ignition engine has been studied, using a square-cross-section single-cylinder engine with two parallel quartz glass walls which permit optical access to the entire cylinder volume. Schlieren short-time exposure photographs and high speed movies were used to define the essential features of this flow. The top-land crevice and the regions behind and between the rings consist of volumes connected through the ring gaps. A system model of volumes and orifices was therefore developed and used to predict the flow into and out of the crevice regions between the piston, piston rings and cylinder wall.

This vehicle simulation study estimates the fuel economy benefits of an HCCI engine system and assesses the NOx, HC and CO aftertreatment performance required for compliance with emissions regulations on U.S. and European regulatory driving cycles. The four driving cycles considered are the New European Driving Cycle, EPA City Driving Cycle, EPA Highway Driving Cycle, and US06 Driving Cycle. For each driving cycle, the following influences on vehicle fuel economy were examined: power-to-weight ratio, HCCI combustion mode operating range, driving cycle characteristics, requirements for transitions out of HCCI mode when engine speeds and loads are within the HCCI operating range, fuel consumption and emissions penalties for transitions into and out of HCCI mode, aftertreatment system performance and tailpipe emissions regulations.

High levels of hydrocarbon emissions during light load operation keep the direct injection stratified charge engine from commercial application. Previous analytical work has identified several possible hydrocarbon emissions mechanisms which can result from poor in-cylinder fuel distribution. Poor fuel distribution can be caused by erratic fuel injection. Experiments conducted on a single cylinder DISC engine show a dramatic increase in the cycle to cycle variation in injection characteristics as engine load decreases. This is accompanied by an increase in cycle to cycle variation in combustion behavior suggesting that degradation in combustion results from the degradation in the quality of the injection event. Examination of combustion and injection characteristics on a cycle by cycle basis shows that, at light load, IMEP and heat release do not correlate with the amount of fuel injected into the cylinder.

In analyzing the processes inside the cylinder of an internal combustion engine, the principal diagnostic at the experimenter's disposal is a measured time history of the cylinder pressure. This paper develops, tests, and applies a heat release analysis procedure that maintains simplicity while including the effects of heat transfer, crevice flows and fuel injection. The heat release model uses a one zone description of the cylinder contents with thermodynamic properties represented by a linear approximation for γ(T). Applications of the analysis to a single-cylinder spark-ignition engine, a special square cross-section visualization spark-ignition engine, and a direct-injection stratified charge engine are presented.

Experiments were performed to identify the knock trends of lean hydrocarbon-air mixtures, and such mixtures enhanced with hydrogen (H2) and carbon monoxide (CO). These enhanced mixtures simulated 15% and 30% of the engine's gasoline being reformed in a plasmatron fuel reformer [1]. Knock trends were determined by measuring the octane number (ON) of the primary reference fuel (mixture of isooctane and n-heptane) supplied to the engine that just produced audible knock. Experimental results show that leaner operation does not decrease the knock tendency of an engine under conditions where a fixed output torque is maintained; rather it slightly increases the octane requirement. The knock tendency does decrease with lean operation when the intake pressure is held constant, but engine torque is then reduced.

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.

When hydrogen is added to a gasoline fueled spark ignition engine the lean limit of the engine can be extended. Lean running engines are inherently more efficient and have the potential for significantly lower NOx emissions. In the engine concept examined here, supplemental hydrogen is generated on-board the vehicle by diverting a fraction of the gasoline to a plasmatron where a partial oxidation reaction is initiated with an electrical discharge, producing a plasmatron gas containing primarily hydrogen, carbon monoxide, and nitrogen. Two different gas mixtures were used to simulate the plasmatron output. An ideal plasmatron gas (H2, CO, and N2) was used to represent the output of the theoretically best plasmatron. A typical plasmatron gas (H2, CO, N2, and CO2) was used to represent the current output of the plasmatron. A series of hydrogen addition experiments were also performed to quantify the impact of the non-hydrogen components in the plasmatron gas.

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 study examines the scaling between engine performance, engine configuration, and engine size and geometry, for modern spark-ignition engines. It focuses especially on design features that impact engine breathing. We also analyze historical trends to illustrate how changes in technology have improved engine performance. Different geometric parameters such as cylinder displacement, piston area, number of cylinders, number of valves per cylinder, bore to stroke ratio, and compression ratio, in appropriate combinations, are correlated to engine performance parameters, namely maximum torque, power and brake mean effective pressure, to determine the relationships or scaling laws that best fit the data. Engine specifications from 1999 model year vehicles sold in the United States were compiled into a database and separated into two-, three-, and four-valves-per-cylinder engine categories.