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The mixture preparation and hydrocarbon (HC) emissions behaviors for a single-cylinder port-fuel-injection SI engine were examined in an engine/dynamometer set up that simulated the first cycle of cranking. The engine was motored continuously at a fixed low speed with the ignition on, and fuel was injected every 8 cycles. Unlike the real engine cranking process, the set up provided a well controlled and repeatable environment to study the cranking process. The parameters were the Engine Coolant Temperature (ECT), speed, and the fuel injection pulse width. The in-cylinder and exhaust HC were measured simultaneously with two Fast-response Flame Ionization Detectors. A large amount of injected fuel (an order of magnitude larger than the normal amount that would produce a stoichiometric mixture in a warm-up engine) was required to form a combustible mixture at low temperatures.

Gasoline HCCI engine has the potential of providing better fuel economy and emissions characteristics than the current SI engines. However, management of HCCI operation for a vehicle is a challenging task. In this paper, the issues of mode transitions between the Spark Ignition and HCCI regimes, and the dynamic nature of the load trajectory within the HCCI regime are considered. Then the phenomena encountered in these operations are illustrated by the data from a single-cylinder engine with electromagnetic-variable-valve timing control. Mode transitions from the SI to HCCI regime may be categorized as robust and non-robust. In a robust transition, every intended HCCI cycle is successful. In a non-robust transition, one or more intended HCCI cycles misfire, although the cycles progress to a satisfactory HCCI operating point in steady state. (The spark ignition was kept on so that the engine could recover from a misfired cycle.)

Homogeneous-Charge-Compression-Ignition (HCCI) engine operation in a vehicle drive cycle is a very dynamic process. In this paper, a controller is devised on the premise that the vehicle is operating under Drive-By-Wire so that the driver commands the engine torque output according to the perceived vehicle speed. Thus a load-following controller is appropriate. Such a controller was developed for a single cylinder engine with electromagnetic variable valve timing control (also known as Controlled-Auto-Ignition (CAI) operation). Under open-loop operation within the CAI regime, the results indicated that the engine response was bipolar in nature: (a) the engine either responded quasi-statically to the open-loop control, or (b) the CAI combustion failed. The latter happened in a load increase process in which the per-cycle increment was too high.

The liquid fuel entry into the cylinder and its subsequent behavior through the combustion cycle were observed by a high speed CCD camera in a transparent engine. The videos were taken with the engine firing under cold conditions in a simulated start-up process, at 1,000 RPM and intake manifold pressure of 0.5 bar. The variables examined were the injector geometry, injector type (normal and air-assisted), injection timing (open- and closed-valve injection), and injected air-to-fuel ratios. The visualization results show several important and unexpected features of the in-cylinder fuel behavior: 1) strip-atomization of the fuel film by the intake flow; 2) squeezing of fuel film between the intake valve and valve seat at valve closing to form large droplets; 3)deposition of liquid fuel as films distributed on the intake valve and head region. Some of the liquid fuel survives combustion into the next cycle.

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.

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 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.

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 performance and heat transfer characteristics of a single cylinder diesel engine in the metal and in the ceramic-coat-insulated configurations were compared at the same speeds, loads and air flow rates. Compared to the metal engine, the insulated engine had a higher brake specific fuel consumption which was attributed to a slower combustion process; the exhaust as well as the time averaged surface temperatures of the insulated engine were higher. The unsteady heat flux amplitudes in the insulated engine were lower which suggested a lower overall heat flux. This lower heat flux was attributed to the lower flame temperatures because of the poor combustion quality in the non-optimized insulated engine.

The heat transfer characteristics of impinging diesel sprays were studied in a Rapid Compression Machine. The temporal and spatial distributions of the heat transfer around the impingement point -were measured by an array of high frequency response surface thermocouples. Simultaneously, the flow field of the combusting spray was photographed with high speed movie through the transparent head of the apparatus. The results for the auto-ignited fuel sprays were compared to those of non-combusting sprays which were carried out in nitrogen. The values of the heat flux from the combusting sprays were found to be substantially different from those of the non-combusting sprays. The difference was attribute to the radiative heat transfer and the combustion generated bulk, motion and small scale turbulence.

A cycle by cycle analysis of engine behavior during the first few cycles of cranking and start-up was performed on a production four-cylinder engine. Experiments were performed to elucidate the effects of initial engine position (rest position after last engine shut-down), first and second cycle fueling, engine temperature, and spark timing on fuel delivery to the cylinder, engine-out Hydrocarbon (EOHC) emissions, and Gross Indicated Mean Effective Pressure (IMEPg). The most important effect of the piston starting position is on the first firing cycle engine rpm, which influences the IMEPg through combustion phasing. Because of the low rpm values for the first cycle, combustion is usually too advanced with typical production engine ignition timing. For both the hot start and the ambient start, the threshold for firing is at an in-cylinder air equivalence ratio (λ) of 1.1.

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.

The fuel effects on HCCI operation in a spark assisted direct injection gasoline engine are assessed. The low load limit has been extended with a pilot fuel injection during the negative valve overlap (NVO) period. The fuel matrix consists of hydrocarbon fuels and various ethanol blends and a butanol blend, plus fuels with added ignition improvers. The hydrocarbon fuels and the butanol blend do not significantly alter the high or the low limits of operation. The HCCI operation appears to be controlled more by the thermal environment than by the fuel properties. For E85, the engine behavior depends on the extent that the heat release from the pilot injected fuel in the NVO period compensates for the evaporative cooling of the fuel.

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.

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 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.

The impact of market-fuel variations on the HCCI operating range was measured in a 2.3L four-cylinder engine, modified for single-cylinder operation. HCCI combustion was achieved through the use of residual trapping. Variable cam phasing was used to maximize the load range at each speed. Test fuels were blended to cover the range of variation in select commercial fuel properties. Within experimental measurement error, there was no change in the low-load limit among the test fuels. At the high-load limit, some small fuel effects on the operating range were observed; however, the observed trends were not consistent across all the speeds studied.

The effects of secondary air on the exhaust oxidation of particulate matters (PM) have been assessed in a direct-injection-spark-ignition engine under fuel rich fast idle condition (1200 rpm; 2 bar NIMEP). Substantial oxidation of the unburned feed gas species (CO and HC) and significant reduction of both the particulate number (up to ∼80%) and volume (up to ∼90%) have been observed. The PM oxidation is attributed to the reactions between the PM and the radicals generated in the oxidation of the feed gas unburned species. This hypothesis is supported by the observation that the reduction in PM volume is proportional to the amount of heat release in the secondary oxidation.

The effects of highly heated fuel on diesel combustion were studied experimentally in a rapid compression machine. A pure fuel, dodecane, heated up to and beyond its critical temperature, was injected into a diesel combustion chamber with the air charge at a compression ratio of 18.2 to 1. The ignition delay was found to decrease with the increase of fuel temperature. The delay decreased to almost zero (within the limit of the accuracy of the instrumentation) at fuel temperatures above 600K. This decrease of delay was explained in terms of a thermal ignition model. For the short ignition delay combustions, the premixed burning phase could not be detected from the heat release data. The mixing controlled burning phases of the heated and unheated fuels however, were not much different; in particular, there was no rapid mixing phenomenon when the fuel temperature was above critical.

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.