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A model for calculating the residual gas fraction in spark ignition engines has been formulated. The model accounts explicitly for the contribution due to the back flow of exhaust gas to the cylinder during the valve overlap period. The model has been calibrated with in-cylinder hydrocarbon measurements at different values of intake pressure, engine speed, and valve overlap timings.

A novel engine management strategy for achieving fast catalyst light-off without the use of an exhaust air pump in a port-fuel-injected, spark ignition engine was developed. A conventional 4-cylinder engine was operated with three cylinders running rich and the fourth one as an air pump to supply air to the exhaust manifold. Under steady-state cold coolant conditions, this strategy achieved near total oxidation of CO and HC with sufficiently retarded spark timing, resulting in a 400% increase in feedgas enthalpy flow and a 90% reduction in feedgas HC emissions compared to conventional operation. The strategy was also evaluated for crank starts. Using the existing engine hardware, implementing the strategy resulted in a reduction in catalyst light-off time from 28.0 seconds under conventional operation to 9.1 seconds.

An adaptive air/fuel ratio controller for SI engine throttle transient was developed. The scheme is based on an event- based, single- parameter fuel dynamics model. A least- square- error algorithm with an active forgetting factor was used for parameter identifications. A one- step- look- ahead controller was designed to maintain the desired air/fuel ratio by canceling the fuel dynamics with the controller setting updated adaptively according to the identified parameters. When implemented on a Ford Ztech engine and tested under a set of throttle- transient operations, the adaptive controller learned quickly and performed well.

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.

The windage tray effect on aeration in the engine sump was assessed by replacing much of the windage tray materials with wire meshes of various blockages. The mesh was to prevent direct impact of the oil drops spinning off the crank shaft onto the sump oil, and simultaneously, to provide sufficient drainage so that there was no significant build up of windage tray oil film that would interact with these droplets. Aeration at the oil pump inlet was measured by X-ray absorption in a production V-6 SI engine motoring at 2000 to 6000 rpm. Within experimental uncertainty, these windage tray changes had no effect on aeration. Thus activities in the sump such as the interaction of the oil drops spun from the crank shaft with the sump oil or with the windage tray, and the agitation of the sump oil by the crank case gas, were not major contributors to aeration at the pump inlet.

The purpose of this work was to develop an understanding of how liquid fuel transported into the cylinder of a port-fuel-injected gasoline-fueled SI engine contributes to hydrocarbon (HC) emissions. To simulate the liquid fuel flow from the valve seat region into the cylinder, a specially designed fuel probe was developed and used to inject controlled amounts of liquid fuel onto the port wall close to the valve seat. By operating the engine on pre-vaporized Indolene, and injecting a small amount of liquid fuel close to the valve seat while the intake valve was open, we examined the effects of liquid fuel entering the cylinder at different circumferential locations around the valve seat. Similar experiments were also carried out with closed valve injection of liquid fuel at the valve seat to assess the effects of residual blowback, and of evaporation from the intake valve and port surfaces.

A research program designed to measure the contribution from fuel absorption in the thin layer of oil, lubricating the cylinder liner, to the total and speciated HC emissions from a spark ignition engine has been performed. The logic of the experiment design was to test the oil layer mechanism via variations in the oil layer thickness (through the lubricant formulations), solubility of the fuel components in the lubricants, and variations in the crankcase gas phase HC concentration (through crankcase purging). A set of preliminary experiments were carried out to determine the solubility and diffusivity of the fuel components in the individual lubricants. Engine tests showed similar HC emissions among the tested lubricants. No consistent increase was observed with oil viscosity (oil film thickness), contrary to what would be expected if fuel-oil absorption was contributing significantly to engine-out HC. Similarly, no effect of crankcase purging could be observed.

The effects of piston top-land crevice size on the indicated net fuel conversion efficiency are assessed in a single cylinder SI engine with 465 cc displacement and 11.2 compression ratio. The operating conditions are at 3.6 and 5.6 bar net indicated mean effective pressure (NIMEP), and at 1500 and 2000 rpm speeds. The cold crevice volume is varied from 524 mm3 to 1331 mm3 by changing the top land height from 3 to 7 mm, and by changing the top-land clearance from 0.247 to 0.586 mm. For a 100 mm3 increase in the top land crevice volume (estimated hot value), the indicated net fuel conversion efficiency decreases by 0.1 percentage point at 1500 rpm, and by 0.13 percentage points at 2000 rpm. The results are not sensitive to the two NIMEP values tested. These values are consistent with a simple crevice filling and discharge/oxidation model.

This paper describes the development of a spark ignition engine operating in a stratified-EGR mode at part load. The concept is to reduce the pumping loss with high levels of EGR while maintaining stable combustion via charge stratification. Since the engine operates stoichiometrically, the ability to control NOx emissions by the three-way catalyst is retained. The configuration of introducing the stoichiometric fresh mixture to the center portion of the combustion chamber with the EGR gas on the two sides is visualized in a transparent engine using planar laser-induced fluorescence (PLIF) and Mie scattering. Visualization results showed that the stratification between air/fuel mixture and EGR gas was relatively well established during the intake stroke. There was, however, significant mixing in the late part of the compression stroke.

The effects of cooled exhaust gas recirculation (EGR) on a boosted direct-injection (DI) spark ignition (SI) engine operating at stoichiometric equivalence ratio, gross indicated mean effective pressure of 14-18 bar, and speed of 1500-2500 rpm, are studied under constant fuel condition at each operating point. In the presence of EGR, burn durations are longer and combustion is more retard. At the same combustion phasing, the indicated specific fuel consumption improves because of a decrease in heat loss and an increase in the specific heat ratio. The knock limited spark advance increases substantially with EGR. This increase is due partly to a slower combustion which is equivalent to a spark retard, as manifested by a retarded value of the 50% burn point (CA50), and due partly to a slower ignition chemistry of the diluted charge, as manifested by the knock limited spark advance to beyond the value offered by the retarded CA50.

The effect of engine operating parameters (speed, spark timing, and fuel-air equivalence ratio [Φ]) on hydrocarbon (HC) oxidation within the cylinder and exhaust system is examined using propane or isooctane fuel. Quench gas (CO2) is introduced at two locations in the exhaust system (exhaust valve or port exit) to stop the oxidation process. Increasing the speed from 1500 to 2500 RPM at MBT spark timing decreases the total, cylinder-exit HC emissions by ∼50% while oxidation in the exhaust system remains at 40% for both fuels. For propane fuel at 1500 rpm, increasing Φ from 0.9 (fuel lean) to 1.1 (fuel rich) reduces oxidation in the exhaust system from 42% to 26%; at 2500 RPM, exhaust system oxidation decreases from 40% to approximately 0% for Φ = 0.9 and 1.1, respectively. Retarded spark increases oxidation in the cylinder and exhaust system for both fuels. Decreases in total HC emissions are accompanied by increased olefinic content and atmospheric reactivity.

The spark ignition engine particulate number (PN) emissions have been correlated to a particulate matter index (PMI) in the literature. The PMI value addresses the fuel effect on PN emission through the individual fuel species reactivity and vapor pressure. The latter quantity is used to account for the propensity of the non-volatile fuel components to survive to the later part of the combustion event as wall liquid films, which serve as sources for particulate emission. The PMI, however, does not encompass the suppression of vaporization by the evaporative cooling of fuel components, such as ethanol, that have high latent heat of vaporization. This paper assesses this evaporative cooling effect on PN emissions by measurements in a GDI engine operating with a base gasoline which does not contain oxygenate, with a blend of the gasoline and ethanol, and with a blend of the gasoline, ethanol, and a hydrocarbon additive so that the blend has the same PMI as the original gasoline.

The combustion behavior in a modem 4-valve engine using a broad range of methanol/gasoline fuel mixtures was studied. The initial flame development was examined by using a spark plug fiber optics probe. Approximately, the kernel expansion speed, Sg, is relatively unchanged from M0 to M40; jumps by ∼30% from M40 to M60; and then remains roughly constant from M60 to M100. Statistics of the IMEP indicate that at a lean idle condition the combustion rate and robustness correlate with Sg: a higher value of Sg gives better combustion. Thus M60-M100 fuels give better idle combustion behavior than the M0-M40 fuels.

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.

The effects of fuel volatility and degree of enrichment on the starting and warm-up behavior of a modern four-valve spark ignition engine with port-fuel-injection were studied. Quantities of interest are the number of cycles to reach first significant firing, the time scale (τr) for the IMEP development, the decay rate of the IMEP fluctuation, and the RMS fluctuation after 3τr. A selected matrix of fuels that included various volume ratios of indolene/MTBE and iso-octane/n-pentane was used. The amount of fuel injected per cycle was varied from stoichiometric to a fuel equivalence ratio of 1.5. The engine behavior (as quantified by the quantities described in the above) is found to correlate well to a single parameter - the fuel equivalence ratio based on the fuel vapor mass calculated from an isothermal equilibrium flash vaporization of the fuel in the vapor boundary layer of the intake flow at intake manifold temperature.

The fuel effects on throttle transients in PFI spark ignition engines were assessed through experiments with simultaneous step change of the throttle position from part load to WOT and increment of the injected fuel amount. The test matrix consisted of various gasoline/methanol blends from pure gasoline to pure methanol, coolant temperatures at 40C (for cold engine condition) and 80C (for warm engine), and different levels of fuel enrichment at the WOT condition. The x-τ model was used to interpret the engine GIMEP response in the transient. Using the model, a procedure was developed to calculate the parameters of the transient from the data. These parameters were systematically regressed against the fuel distillation points, the increment in injected fuel mass in the transient, and the enthalpy required to evaporate the fuel increment as the explanatory variables.

An ignition delay correlation encompassing the effects of temperature, pressure, residual gas, EGR, and lambda (on both the rich and lean sides) has been developed. The procedure uses the individual knocking cycle data from a boosted direct injection SI engine (GM LNF) operating at 1250 to 2000 rpm, 8-14 bar GIMEP, EGR of 0 to 12.5%, and lambda of 0.8 to 1.3 with a certification fuel (Haltermann 437, with RON=96.6 and MON=88.5). An algorithm has been devised to identify the knock point on individual pressure traces so that the large data set (of some thirty three thousand cycles) could be processed automatically. For lean and for rich operations, the role of the excess fuel, air, and recycled gas (which has excess air in the lean case, and hydrogen and carbon monoxide in the rich case) may be treated effectively as diluents in the ignition delay expression.

The residual gas fraction prior to ignition at the vicinity of the spark plug in a single cylinder, two-valve spark ignition engine was measured with a fast-response flame ionization hydrocarbon detector. The technique in using such an instrument is reported. The measurements were made as a function of the intake manifold pressure, engine speed and intake/exhaust valve-overlap duration. Both the mean level of the residual fraction and the statistics of the cycle-to-cycle variations were obtained.

The effects of the directed port flow produced by a Charge-Motion-Control-Valve (CMCV) on mixture preparation in a Port-Fuel-Injection engine were assessed under conditions typical of fast idle in a cold start process. The port fuel was found to comprise two components: a “valve” puddle (at the vicinity of the valve) that built up quickly, and that was mainly responsible for the delivery of the fuel to the cylinder charge; a “port” puddle located significantly upstream. The latter was mainly created by the reverse back flow process and built up slowly. Although the fuel amounts in these two components were roughly the same, the latter did not significantly interact with the fuel transport to the cylinder charge. The CMCV only weakly affected the purging or filling time of the valve puddle, hence the dynamics of the fuel delivery process was not materially affected.

The flow and heat transfer phenomena in the intake port of a spark ignition engine with port fuel injection play a significant role in the mixture preparation process, especially at part load. The backflow of the hot burned gas from the cylinder into the intake port when the intake valve is opened breaks up any liquid film around the inlet valve, influences gas and wall temperatures, and has a major effect on the fuel vaporization process. The backflow of in-cylinder mixture with its residual component during the compression stroke prior to inlet valve closing fills part of the port with gas at higher than fresh mixture temperature. To quantify these phenomena, time-resolved measurements of the hydrocarbon concentration profile along the center-line of the intake port were made with a fast-response flame ionization detector, and of the gas temperature with a fine wire resistance thermometer, in a single-cylinder engine running with premixed propane/air mixture.