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A single-zone burn-rate analysis based on measured cylinder pressure data proposed by Gatowski et al. in 1984 was evaluated over the full load and speed range of a spark-ignition engine. The analysis, which determines the fuel mass burning rate based on the First Law of Thermodynamics, includes sub-models for the effects of residual fraction, heat transfer, and crevices. Each of these sub-models was assessed and calibrated. Cylinder pressure data over the full engine operating range obtained from two different engines were used to examine the robustness of the analysis. The sensitivity of predictions to the parameters wall temperature, heat transfer model coefficients and exponent, swirl ratio, motoring polytropic constant, in-cylinder mass, and to uncertainty in pressure data was evaluated.

This paper provides an overview of spark-ignition engine unburned hydrocarbon emissions mechanisms, and then uses this framework to relate measured engine-out hydrocarbon emission levels to the processes within the engine from which they result. Typically, spark-ignition engine-out HC levels are 1.5 to 2 percent of the gasoline fuel flow into the engine; about half this amount is unburned fuel and half is partially reacted fuel components. The different mechanisms by which hydrocarbons in the gasoline escape burning during the normal engine combustion process are described and approximately quantified. The in-cylinder oxidation of these HC during the expansion and exhaust processes, the fraction which exit the cylinder, and the fraction oxidized in the exhaust port and manifold are also estimated.

To understand the effects of crevices on the engine-out hydrocarbon emissions, a series of engine experiments was carried out with different piston crevice volumes and with simulated head gasket crevices. The engine-out HC level was found to be modestly sensitive to the piston crevice size in both the warmed-up and the cold engines, but more sensitive to the crevice volume in the head gasket region. A substantial decrease in HC in the cold-to-warm-up engine transition was observed and is attributed mostly to the change in port oxidation.

A method for determining the flame contour based on the flame arrival time at the fiber optic (FO) spark plug and at the head gasket ionization probe (IP) locations has been developed. The experimental data were generated in a single-cylinder Ricardo Hydra spark-ignition engine. The head gasket IP, constructed from a double-sided copper-clad circuit board, detects the flame arrival time at eight equally spaced locations at the top of the cylinder liner. Three other IP's were also installed in the cylinder head to provide additional intermediate data on flame location and arrival time. The FO spark plug consists of a standard spark plug with eight symmetrically spaced optical fibers located in the ground casing of the plug. The cylinder pressure was recorded simultaneously with the eleven IP signals and the eight optical signals using a high-speed PC-based data acquisition system.

A model which converts flame arrival times at a head gasket ionization probe, used in a spark-ignition engine, into flame contours has been developed. The head gasket was manufactured at MIT using printed circuit board techniques. It has eight electrodes symmetrically spaced around the circumference (top of cylinder liner) and it replaces the conventional head gasket. The model is based on engine flame propagation rate data taken from the literature. Data from optical studies of S.I. engine combustion or studies utilizing optical fiber or ionization probe diagnostics were analyzed in terms of the apparent flame speed and the entrainment speed (flame speed relative to the fluid ahead of the flame). This gives a scaling relationship between the flame speed and the mass fraction burned which is generic and independent of the chamber shape.

A model has been developed which predicts engine-out hydrocarbon (HC) emissions for spark-ignition engines. The model consists of a set of scaling laws that describe the individual processes that contribute to HC emissions. The model inputs are the critical engine design and operating variables. This set of individual process scaling relations was then calibrated using production spark-ignition engine data at a fixed light-load operating point. The data base consisted of engine-out HC emissions from two-valve and four-valve engine designs with variations in spark timing, valve timing, coolant temperature, crevice volume, and EGR, for five different engines. The model was calibrated separately for the three different engines to accommodate differences in engine design details and to determine the relative magnitudes of each of the major sources. A good fit to this database was obtained.

A computational fluid dynamics (CFD) prediction of the transient flow in the intake system of a spark ignition engine is compared to experimental data. The calculation was performed for a single cylinder version of a pre-1995 Ford two-valve production engine, while experiments were carried out on a single cylinder Ricardo Mark 3 research engine with similar overall geometric parameters. While the two engines have somewhat different geometries, this was not considered to be a significant problem for our study of flow features. Both set-ups employed gaseous fuel. The calculation was performed using the commercially available Star-CD code incorporating the complete intake manifold runner and cylinder into the mesh. Cylinder pressures were in good agreement with experiment indicating that wave dynamics were well captured. Comparison was also made to the measured instantaneous gas temperatures along the intake system.

A complete one-dimensional mixed lubrication model has been developed to predict oil film thickness and friction of the piston ring-pack. An average flow model and a roughness contact model are used to consider the effects of surface roughness on both hydrodynamic and boundary lubrication. Effects of shear-thinning and liner temperature on lubricant viscosity are included. An inlet condition is applied by considering the unsteady wetting location at the leading edge of the ring. A ‘film non-separation’ exit condition is proposed to replace Reynolds exit condition when the oil squeezing becomes dominant. Three lubrication modes are considered in the model, namely, pure hydrodynamic, mixed, and pure boundary lubrication. All of these considerations are crucial for studying the oil transport, asperity contact, and friction especially in the top dead center (TDC) region where the oil control ring cannot reach.

This paper describes the use of a modified quasi-dimensional spark-ignition engine simulation code to predict the extent of cycle-to-cycle variations in combustion. The modifications primarily relate to the combustion model and include the following: 1. A flame kernel model was developed and implemented to avoid choosing the initial flame size and temperature arbitrarily. 2. Instead of the usual assumption of the flame being spherical, ellipsoidal flame shapes are permitted in the model when the gas velocity in the vicinity of the spark plug during kernel development is high. Changes in flame shape influence the flame front area and the interaction of the enflamed volume with the combustion chamber walls. 3. The flame center shifts due to convection by the gas flow in the cylinder. This influences the flame front area through the interaction between the enflamed volume and the combustion chamber walls. 4. Turbulence intensity is not uniform in cylinder, and varies cycle-to-cycle.

A method to collect and speciate the components of gasoline absorbed in the lubricant oil using gas chromatography has been developed. Samples were collected continuously from the piston skirt, baffle and sump in a Saturn engine. A long (18 hours) test was performed to determine the build up of hydrocarbons in the sump, and a shorter (25 min) test was performed to determine the build up of hydrocarbons in the piston skirt and baffle during engine warm-up. The first experiment showed that the total hydrocarbon concentration in the sump oil reached a steady state of about 1.35% mass fraction after 11 hours of engine operation. The relative concentration of individual fuel hydrocarbon species absorbed in the oil increases exponentially with boiling point. Most of the identified species in the oil consist of the heavy end aromatics. Similar compositions but lower concentrations were found for samples collected from the piston skirt during engine warm-up.

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.

The wear patterns of the rings and grooves of a diesel engine were analyzed by using a ring dynamics/gas flow model and a ring-pack oil film thickness model. The analysis focused primarily on the contact pressure distribution on the ring sides and grooves as well as on the contact location on the ring running surfaces. Analysis was performed for both new and worn ring/groove profiles. Calculated results are consistent with the measured wear patterns. The effects of groove tilt and static twist on the development of wear patterns on the ring sides, grooves, and ring running surfaces were studied. Ring flutter was observed from the calculation and its effect on oil transport was discussed. Up-scraping of the top ring was studied by considering ring dynamic twist and piston tilt. This work shows that the models used have potential for providing practical guidance to optimizing the ring pack and ring grooves to control wear and reduce oil consumption.

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.

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.

An experimental study was performed to determine the fraction of unburned hydrocarbon emissions which are oxidized in the exhaust port of a spark ignition engine. The technique used was injection of a CO2 quench gas into the exhaust port, at various planes along the port centerline, to cool the exhaust gas and “freeze” the hydrocarbon oxidation reactions. By quenching the reaction of hydrocarbons at the cylinder exit plane, cylinder exit hydrocarbon emissions levels were determined. By differencing the concentration of hydrocarbons observed during quenching and nonquenching operation, the fraction of hydrocarbons reacting in each section of the exhaust was determined. Experiments were carried out to define the effects of engine operating conditions on the fraction of hydrocarbons oxidized. The variables studied were fuel-air equivalence ratio, speed, load, spark advance and compression ratio.

Photographic and performance studies with a Rapid Compression Machine at the Massachusetts Institute of Technology have been used to develop insight into the role of mixing in diesel engine combustion. Combustion photographs and performance data were analyzed. The experiments simulate a single fuel spray in an open chamber diesel engine with direct injection. The effects of droplet formation and evaporation on mixing are examined. It is concluded that mixing is controlled by the rate of entrainment of air by the fuel spray rather than the dynamics of single droplets. Experimental data on the geometry of a jet in a quiescent combustion chamber were compared with a two-phase jet model; a jet model based on empirical turbulent entrainment coefficients was developed to predict the motion of a fuel jet in a combustion chamber with swirl. Good agreement between theory and experiment was obtained.

The design and operating characteristics of a single-cylinder transparent spark-ignition engine for Schlieren flow visualization are described. The engine is built on a CFR engine crankcase using the CFR piston and cylinder as a crosshead for the square cross-section piston and cylinder assembly. The square cross-section assembly has two parallel steel walls and two parallel quartz glass walls to permit optical access to the entire cylinder volume over the complete engine operating cycle. The CFR head and valve mechanism completes the assembly. It is shown that the engine operates satisfactorily with propane fuel under typical engine operating conditions. Schlieren short time-exposure photographs and high speed movies were taken to define details of the flow and density fields through the engine cycle. Photographs which illustrate key features of these fields are presented and described.

A computer simulation of the four-stroke spark-ignition engine cycle has been used to examine the effects of turbocharging and reduced heat transfer on engine performance, efficiency and NOx emissions. The simulation computes the flows into and out of the engine, calculates the changes in thermodynamic properties and composition of the unburned and burned gas mixtures within the cylinder through the engine cycle due to work, heat and mass transfers, and follows the kinetics of NO formation and decomposition in the burned gas. The combustion process is specified as an input to the program through use of a normalized rate of mass burning profile. From this information, the simulation computes engine power, fuel consumption and NOx emissions. Wide-open-trottle predictions made with the simulation were compared with experimental data from a 5.7ℓ naturally-aspirated and a 3.8ℓ turbocharged production engine.

This paper describes the results of experimental and computer simulation studies of the combustion process in the prechamber three-valve stratified-charge engine. Prechamber and main-chamber pressure data and matched computer simulation calculations are used to determine the effects of variations in overall air/fuel ratio, engine speed and load, and prechamber volume and orifice diameter on the parameters which define the combustion process (spark advance for optimum torque, ignition delay, combustion duration), on cylinder pressure diagrams (mean main-chamber pressure, mean pressure difference across the orifice, and cycle-by-cycle pressure fluctuations) and on exhaust emissions. General correlations are derived from the data for the shape of the combustion rate profile and the extent of the combustion duration.