Search Results

An experimental study was performed in a firing SI engine at conditions representative of the warmup phase of operation in which liquid gasoline films were established at various locations in the combustion chamber and the resulting impact on hydrocarbon emissions was assessed. Unique about this study was that it combined, in a firing engine environment, direct visual observation of the liquid fuel films, measurements of the temperatures these films were subjected to, and the determination from gas analyzers of burned and unburned fuel quantities exiting the combustion chamber - all with cycle-level resolution or better. A means of deducing the exhaust hydrocarbon emissions that were due to the liquid fuel films in the combustion chamber was developed. An increase in exhaust hydrocarbon emissions was always observed with liquid fuel films present in the combustion chamber.

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.

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.

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.

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.

An experimental study was carried out that qualitatively examined the mixture preparation process in port fuel injected engines. The primary variables in this study were intake valve lift, intake valve timing, injector spray quality, and injection timing. A special visualization engine was used to obtain high-speed videos of the fuel-air mixture flowing through the intake valve, as well as the wetting of the intake valve and head in the combustion chamber. Additionally, videos were taken from within the intake port using a borescope to examine liquid fuel distribution in the port. Finally, a simulation study was carried out in order to understand how the various combinations of intake valve lifts and timings affect the flow velocity through the intake valve gap to aid in the interpretation of the videos.

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.

As a part of the effort to comply with increasingly stringent emission standards, engine manufacturers strive to minimize engine oil consumption. This requires the advancement of the understanding of the characteristics, sources, and driving mechanisms of oil consumption. This paper presents a combined theoretical and experimental approach to separate and quantify different oil consumption sources in a production spark ignition engine at different speed and load conditions. A sulfur tracer method was used to measure the dependence of oil consumption on engine operating speed and load. Liquid oil distribution on the piston was studied using a Laser-Induced-Fluorescence (LIF) technique. In addition, important in-cylinder parameters for oil transport and oil consumption, such as liner temperatures and land pressures, were measured.

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.

Engine oil consumption is an important source of hydrocarbon and particulate emissions in automotive engines. Oil evaporating from the piston-ring-liner system is believed to contribute significantly to total oil consumption, especially during severe operating conditions. This paper presents an extensive experimental and theoretical study on the contribution of oil evaporation to total oil consumption at different steady state speed and load conditions. A sulfur tracer method was used to measure the dependence of oil consumption on coolant outlet temperature, oil volatility, and operating speed and load in a production spark ignition engine. Liquid oil distribution on the piston was studied using a one-point Laser-Induced-Fluorescence (LIF) technique. In addition, important in-cylinder variables for oil evaporation, such as liner temperature and cylinder pressure, were measured. A multi-species cylinder liner oil evaporation model was developed to interpret the oil consumption data.

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.

A gasoline direct injection fuel spray was observed using a fired, optical access, square cross-section single cylinder research engine and high-speed video imaging. Spray interaction with the piston is described qualitatively, and the results are compared with Computational Fluid Dynamics (CFD) simulation results using KIVA-3V version 2. CFD simulations predicted that within the operating window for stratified charge operation, between 1% and 4% of the injected fuel would remain on the piston as a liquid film, dependent primarily on piston temperature. The experimental results support the CFD simulations qualitatively, but the amount of fuel film remaining on the piston appears to be under-predicted. High-speed video footage shows a vigorous spray impingement on the piston crown, resulting in vapor production.

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.

Liquid fuel behavior in the cylinder impacts SI engine HC emissions particularly during engine start-up. Inflow of liquid fuel into the cylinder is largely determined by the flow and temperature environment in the intake port. Subsequent evaporation of fuel droplets in the cylinder prior to impact on the piston and cylinder liner reduces the amount of liquid fuel in the cylinder that is likely to contribute to HC emission and is therefore important. In this study, measurements of liquid fuel droplet characteristics in the vicinity of the intake valve of a firing SI engine were analyzed to estimate the amount and spatial distribution of in-cylinder evaporation of liquid fuel prior to droplet impact on the cylinder liner or piston. A one-dimensional fuel droplet evaporation model was developed to predict the amount of fuel evaporation given measured fuel droplet sizes and velocities, intake port and valve temperatures during warm up, and cylinder geometry.

Liquid fuel inflow into the cylinder is considered to be an important source of exhaust hydrocarbon (HC) emissions from automotive spark ignition engines. These liquid-fuel-caused emissions are increased significantly during the start up and subsequent warm-up period. This study analyzes the influence of several engine and injector design variables, and fuel parameters, on the in-cylinder liquid fuel behavior. The effect of the following parameters on the characteristics of the fuel droplets entering the cylinder was studied: Fuel volatility, injection timing, intake valve timing, injector type, spray geometry, and spray targeting in the intake port. A Phase Doppler Particle Analyzer (PDPA) was used in a single-cylinder flow visualization combustion engine to assess this in-cylinder liquid fuel behavior. Measurements of fuel droplet characteristics (size and velocity) were taken in selected locations in the vicinity of the intake valve during starting and warm up.

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.

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.

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.

The occurrence of liquid fuel in the cylinder of automotive internal combustion engines is believed to be an important source of exhaust hydrocarbon (HC) emissions, especially during the warm-up process following an engine start up. In this study a Phase Doppler Particle Analyzer (PDPA) has been used in a transparent flow visualization combustion engine in order to investigate the phenomena which govern the transport of liquid fuel into the cylinder during a simulated engine start up process. Using indolene fuel, the engine was started up from room temperature and run for 90 sec on each start up simulation. The size and velocity of the liquid fuel droplets entering the cylinder were measured as a function of time and crank angle position during these start up processes. The square-piston transparent engine used gave full optical access to the cylinder head region, so that these droplet characteristics could be measured in the immediate vicinity of the intake valve.