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The fuel injection process in the port of a firing 4-valve SI engine at part load and 25°C head temperature was observed by a high speed video camera. Fuel was injected when the valve was closed. The reverse blow-down flow when the intake valve opens has been identified as an important factor in the mixture preparation process because it not only alters the thermal environment of the intake port, but also strip-atomizes the liquid film at the vicinity of the intake valve and carries the droplets away from the engine. In a series of “fuel-on” experiments, the fuel injected in the current cycle was observed to influence the fuel delivery to the engine in the subsequent cycles.

A sampling system was developed to measure the evolution of the speciated hydrocarbon emissions from a single-cylinder SI engine in a simulated starting and warm-up procedure. A sequence of exhaust samples was drawn and stored for gas chromatograph analysis. The individual sampling aperture was set at 0.13 s which corresponds to ∼ 1 cycle at 900 rpm. The positions of the apertures (in time) were controlled by a computer and were spaced appropriately to capture the warm-up process. The time resolution was of the order of 1 to 2 cycles (at 900 rpm). Results for four different fuels are reported: n-pentane/iso-octane mixture at volume ratio of 20/80 to study the effect of a light fuel component in the mixture; n-decane/iso-octane mixture at 10/90 to study the effect of a heavy fuel component in the mixture; m-xylene and iso-octane at 25/75 to study the effect of an aromatics in the mixture; and a calibration gasoline.

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.

The effects of charge motion and laminar flame speeds on combustion and exhaust temperature have been studied by using an air jet in the intake flow to produce an adjustable swirl or tumble motion, and by replacing the nitrogen in the intake air by argon or CO₂, thereby increasing or decreasing the laminar flame speed. The objective is to examine the "Late Robust Combustion" concept: whether there are opportunities for producing a high exhaust temperature using retarded combustion to facilitate catalyst warm-up, while at the same time, keeping an acceptable cycle-to-cycle torque variation as measured by the coefficient of variation (COV) of the net indicated mean effective pressure (NIMEP). The operating condition of interest is at the fast idle period of a cold start with engine speed at 1400 RPM and NIMEP at 2.6 bar. A fast burn could be produced by appropriate charge motion. The combustion phasing is primarily a function of the spark timing.

The combustion process after auto-ignition is investigated. Depending on the non-uniformity of the end gas, auto-ignition could initiate a flame, produce pressure waves that excite the engine structure (acoustic knock), or result in detonation (normal or developing). For the “acoustic knock” mode, a knock intensity (KI) is defined as the pressure oscillation amplitude. The KI values over different cycles under a fixed operating condition are observed to have a log-normal distribution. When the operating condition is changed (over different values of λ, EGR, and spark timing), the mean (μ) of log (KI/GIMEP) decreases linearly with the correlation-based ignition delay calculated using the knock-point end gas condition of the mean cycle. The standard deviation σ of log(KI/GIMEP) is approximately a constant, at 0.63. The values of μ and σ thus allow a statistical description of knock from the deterministic calculation of the ignition delay using the mean cycle properties

Engine Hydrocarbon (HC) emissions behaviors in the shut down and re-start processes were examined in a production 4-cylinder 2.4 L engine. Depending on when the power to the ECU was cut off relative to the engine events, there could be two or three mis-fired cylinders (i.e. cylinders with fuel injected but no ignition). The total HC pumped out by the engine into the catalyst in the stopping process was ∼ 4 mg (approximately equaled to the amount of one injection at idle condition). Because the size of the catalyst was larger than the total exhaust volume in the stopping process, this HC was not observed at the catalyst exit. The catalyst temperature was also not affected. When the engine was purged after shut down (by cranking the engine with the injectors and ignition disconnected), the total exit HC was 33 mg. In a restart 90 minutes after shut down, the integrated amount of HC emissions due to residual fuel from the stopping process was 16 mg.

The engine and its exhaust flow behaviors are investigated in a turbo-charged gasoline direct injection engine under simulated cold-fast-idle condition. The metrics of interest are the exhaust sensible and chemical enthalpy flows, and the exhaust temperature, all of which affect catalyst light off time. The exhaust sensible enthalpy flow is mainly a function of combustion phasing; the exhaust chemical enthalpy flow is mainly a function of equivalence ratio. High sensible and chemical enthalpy flow with acceptable engine stability could be obtained with retarded combustion and enrichment. When split injection is employed with one early and one later and smaller fuel pulse, combustion retards with early secondary injection in the compression stroke but advances with late secondary injection. Comparing gasoline to E85, the latter produces a lower exhaust temperature because of charge cooling effect and because of a faster combustion.

This work examines the effect of valve timing during cold crank-start and cold fast-idle (1200 rpm, 2 bar NIMEP) on the emissions of hydrocarbons (HC) and particulate mass and number (PM/PN). Four different cam-phaser configurations are studied in detail: 1. Baseline stock valve timing. 2. Late intake opening/closing. 3. Early exhaust opening/closing. 4. Late intake phasing combined with early exhaust phasing. Delaying the intake valve opening improves the mixture formation process and results in more than 25% reduction of the HC and of the PM/PN emissions during cold crank-start. Early exhaust valve phasing results in a deterioration of the HC and PM/PN emissions performance during cold crank-start. Nevertheless, early exhaust valve phasing slightly improves the HC emissions and substantially reduces the particulate emissions at cold fast-idle.

When gas sample is continuously drawn from the cylinder of an internal combustion engine, the sample that appears at the end of the sampling system corresponds to the in-cylinder content sometime ago because of the finite transit time which is a function of the cylinder pressure history. This variable delay causes a dispersion of the sample signal and makes the interpretation of the signal difficult An unsteady flow analysis of a typical sampling system was carried out for selected engine loads and speeds. For typical engine operation, a window in which the delay is approximately constant may be found. This window gets smaller with increase in engine speed, with decrease in load, and with the increase in exit pressure of the sampling system.

Particulate emissions from a production gasoline direct injection spark ignition engine were studied under a typical cold-fast-idle condition (1200 rpm, 2 bar NIMEP). The particle number (PN) density in the 22 to 365 nm range was measured as a function of the injection timing with single pulse injection and with split injection. Very low PN emissions were observed when injection took place in the mid intake stroke because of the fast fuel evaporation and mixing processes which were facilitated by the high turbulent kinetic energy created by the intake charge motion. Under these conditions, substantial liquid fuel film formation on the combustion chamber surfaces was avoided. PN emissions increased when injection took place in the compression stroke, and increased substantially when the fuel spray hit the piston.

The high load limit of a boosted homogeneous-charge-compression-ignition (HCCI) engine operating on negative-valve-overlap (NVO) was assessed. When operating under stoichiometric condition with no external dilution, the load, as measured by the net indicated mean effective pressure (NIMEP), increased with increase in manifold absolute pressure (MAP), and with decrease in trapped amount of residual gas. The maximum pressure rise rate (MPRR), however, also increased correspondingly. When the MAP and the amount of residual gas were adjusted so that the engine operating point could be held at a constant MPRR value, the NIMEP increased with the simultaneous decrease in MAP and residual until the misfire limit was reached. Therefore if a MPRR ceiling is imposed, the high load limit of an HCCI engine is at the intersection of the constraining MPRR line and the misfire line.

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.)

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 catalyst oxygen storage capacities were measured over a test matrix consisted of fuels with 7, 33, 266 and 500 ppm sulfur, and of dynamometer-aged catalysts simulating 4K, 50K and 150K vehicle miles. A methodology was developed to relate the post-catalyst λ sensor response following an engine lean-step-transient to the total oxygen storage sites available. The time resolved NOx concentration profiles (which were most sensitive to the oxygen storage) in the catalyst were measured with the engine operating at λ modulations of various amplitudes and frequencies. The oxygen storage capacity deterioration comprised two multiplicative factors - an age factor which decreased quickly initially (by a factor of 2 from 4K to 50K miles), and then more modestly (by 30% from 50 to 150K miles), and a fuel sulfur factor which decreased by 10% for every 150 ppm increase in sulfur level.

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 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 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 interaction of intake port gas flow with the fuel spray in a port-fuel-injection engine is studied to see whether there are opportunities to facilitate the mixture preparation process and to improve the HC emissions through this interaction. The operating regime of interest is the fast idle period in a cold start. For single pulse injection, the HC emissions were not sensitive to injection details for closed-valve injection; emissions increased with open-valve injection. Then a split injection strategy was used in which the fuel was divided into two pulses. The first pulse was delivered during valve-closed; the second pulse was injected in the back flow period. Under cold-valve conditions, a small benefit (compared to close valve injection) was obtained with a second pulse fuel of 25%: 6% decrease in Specific HC emissions and 4.5% increase in the fuel delivery fraction.

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.