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A conventional coil ignition system and two breakdown ignition systems with different electrode configurations were compared in M.I.T.'s transparent square piston engine. The purpose was to gain a deeper understanding of how the breakdown and glow discharge phases affect flame development and engine performance. The engine was operated with a standard intake valve and with a shrouded intake valve to vary the characteristic burning rate of the engine. Cylinder pressure data were used to characterize the ignition-system performance. A newly developed schlieren system which provides two orthogonal views of the developing flame was used to define the initial flame growth process. The study shows that ignition systems with higher breakdown energy achieve a faster flame growth during the first 0.5 ms after spark onset for all conditions studied.

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.

An analysis method for characterizing fuel behavior during spark-ignition engine starting has been developed and applied to several sets of start-up data. The data sets were acquired from modern production vehicles during room temperature engine start-up. Two different engines, two control schemes, and two engine temperatures (cold and hot) were investigated. A cycle-by-cycle mass balance for the fuel was used to compare the amount of fuel injected with the amount burned or exhausted as unburned hydrocarbons. The difference was measured as “fuel unaccounted for”. The calculation for the amount of fuel burned used an energy release analysis of the cylinder pressure data. The results include an overview of starting behavior and a fuel accounting for each data set Overall, starting occurred quickly with combustion quality, manifold pressure, and engine speed beginning to stabilize by the seventh cycle, on average.

The direct injection spark-ignition engine is the only internal combustion engine with the potential to equal the efficiency of the diesel and to tolerate a wide range of fuel types and fuel qualities without deterioration of performance. However, this engine has low combustion efficiency and excessive hydrocarbon emissions when operating at light load. In this paper, potential sources of hydrocarbon emissions during light load operation are postulated and analyzed. The placement of fuel away from the primary combustion process in conjunction with a lack of secondary burnup are isolated as important hydrocarbon emissions mechanisms. Analyses show that increasing cylinder gas temperatures can improve secondary burnup of fuel which would reduce hydrocarbon emissions. Practical means to achieve this include higher compression ratio and use of ceramic parts in the combustion chamber.

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.

An experimental study was conducted on a direct-injection stratified-charge (DISC) engine incorporating a combustion process similar to the Texaco Controlled Combustion System and operated with gasoline. Analysis of the injected fuel flow and the heat release showed that the combustion process was characterized by three distinct phases: fuel injection and distribution around the piston bowl, flame propagation through the stratified fuel-air mixture, and mixing-controlled burn-out with the heat-release rate proportional to the amount of unburned fuel in the combustion chamber. This characterization was consistent with previous visualization studies conducted on rapid-compression machines with similar configurations. Experiments with varied injection timing, spark plug location, and spark timing showed that the combustion timing relative to injection was critical to the hydrocarbon emissions from the engine.

NO2 is an effective soot oxidizer operating at lower temperatures than O2. The effect of pure NO2 on soot oxidation was evaluated and compared with the gas treated by plasma, which initially consisted of NO, O2, and hydrocarbons. The cutout of a commercial DPF was used and the pressure difference across the DPF was monitored for an hour. The concentration of NO/NO2, CO, CO2 at the outlet of the DPF was measured as a function of time. CO and CO2 concentration was measured periodically by gas chromatography. The experiment was performed at 230, 250, 300, 350°C. When NO2 only was used as an oxidizing agent, there was a close relationship between the decrease of the pressure difference across the DPF, the CO and CO2 concentration at the outlet of the DPF, and the back conversion of NO2 to NO.

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.

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.

Effect of various hydrocarbons on the plasma DeNOx process in simulated diesel engine operating conditions is investigated experimentally and theoretically. This paper shows the results of an extensive series of experiments on the NOx conversion effect of various hydrocarbons (methane, ethene, propene, propane) in the plasma. The effects of energy density, temperature, and the initial concentrations of hydrocarbon and oxygen are discussed and the results for each hydrocarbon are compared with one another. The energy required to convert one NO molecule is measured 13.8eV, 16.1eV, 23.2eV, 45.6eV for propene, ethene, propane, methane, respectively when energy density of 25.4J/L is delivered to the mixture of 10% O2, base N2 with 440ppm NO and 500ppm hydrocarbon at 473K, while it is 143.2eV without hydrocarbon. The best NOx conversion effect of propene among the mentioned hydrocarbons is due to the highest reaction rates of propene with O and OH.

An experimental study was performed to investigate the effects of various intake charge motion control valves (CMCVs) on mixture preparation, combustion, and hydrocarbon (HC) emissions during the cold start-up process of a port fuel injected spark ignition (SI) engine. Different charge motions were produced by three differently shaped plates in the CMCV device, each of which blocked off 75% of the engine's intake ports. Time-resolved HC, CO and CO2 concentrations were measured at the exhaust port exit in order to achieve cycle-by-cycle engine-out HC mass and in-cylinder air/fuel ratio. Combustion characteristics were examined through a thermodynamic burn rate analysis. Cold-fluid steady state experiments were carried out with the CMCV open and closed. Enhanced charge motion with the CMCV closed was found to shorten the combustion duration, which caused the location of 50% mass fraction burned (MFB) to occur up to 5° CA earlier for the same spark timing.

LDA measurements of the flow in a motored engine near TDC of compression have been obtained, along with burnrate data in a firing engine having a near-central spark plug location. Results are reported for two different intake ports and four intake valve lifts varying from 25% to 100% of full lift. Opposite trends of swirl vs valve lift were found for the two ports, and the rms velocity fluctuation was found to be relatively insensitive to changes in valve lift. Regression analysis of the burn duration data was conducted, with swirl ratio and rms as independent variables. The analysis indicated that burn duration decreases with an increase in swirl ratio and/or rms velocity fluctuation. In light of the experimental findings, a new conceptual model is proposed regarding the effect of valve lift on the dissipation of turbulent velocity via changes in the length scale.

Experiments were conducted to determine the effects of substantial spark retard on combustion, hydrocarbon (HC) emissions, and exhaust temperature, under cold engine conditions. A single-cylinder research engine was operated at 20° C fluid temperatures for various spark timings and relative air/fuel ratios. Combustion stability was observed to decrease as the phasing of the 50% mass fraction burned (MFB) occurred later in the expansion stroke. A thermodynamic burn rate analysis indicated combustion was complete at exhaust valve opening with -20° before top dead center (BTDC) spark timings. Chemical and thermal energy of the exhaust gas was tracked from cylinder-exit to the exhaust runner. Time-resolved HC concentrations measured in the port and runner were mass weighted to obtain an exhaust HC mass flow rate. Results were compared to time averaged well downstream HC levels.

The effects of two commonly used methods for altering the combustion process in a spark-ignition engine are examined using pressure measurements and high-speed schlieren photography. A square cross-section visualization engine with two quartz sidewalls was used to allow optical access over the entire four-stroke operating cycle. Engine operation with a shrouded intake valve, which changed the intake-generated flow, and with a stepped piston, which changed the compression-generated flow, are compared to a base condition. In addition, cyclic variations in burning are examined for all cases.

Two features to facilitate chemical reactions at low temperature, non-thermal plasma and the weak dependency of photocatalyst on temperature, have been exploited by many researchers to effectively decompose hydrocarbon emissions emitted until the light-off of a three-way catalyst in spark ignition engines. To develop a realizable emissions reduction reactor, as part of such effort, this study investigates for the three model gases, propylene, n-butane and acetylene: 1) the conversion efficiency of the emissions reduction reactor, which utilizes the effect of dissociation, ionization-by-collision of the non-thermal plasma and the photocatalytic effect of TiO2, and 2) the concentrations of the products such as acetaldehyde, acetic acid, polymerized hydrocarbons and NO2. The operating parameters to obtain the plasma energy density ranging from 7.8 to 908 J/L were varied.

A model for predicting the performance and emissions characteristics of Wankel engines has been developed and tested. Each chamber is treated as an open thermodynamic system and the effects of turbulent flame propagation, quench layer formation, gas motion, heat transfer and seal leakage are included. The experimental tests were carried out on a Toyo Kogyo 12B engine under both motoring and firing conditions and values for the effective seal leakage area and turbulent heat transfer coefficient were deduced. The agreement between the predicted and measured performances was reasonable. Parametric studies of the effects of reductions in seal leakage and heat transfer were carried out and the results are presented.

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.

Flame propagation was detected with ionization probes located at a spark plug and a head gasket to study the relations of ionization signal to the flame propagation period. Five ionization probes were inserted at a spark plug to detect the initial flame development and eight ionization probes were inserted at a head gasket to detect the overall flame propagation. Experiments were done while the A/F ratio, load and engine speed were varied. In the fast acceleration period, lean peak phenomenon due to the fuel wall wetting occurred for one or two cycles. Ionization signals were used to determine the flame propagation duration during fast acceleration and the lean peak could be avoided by injecting proper amount of fuel.

The flow into and out of the piston top-land crevice of a spark-ignition engine has been studied, using a square-cross-section single-cylinder engine with two parallel quartz glass walls which permit optical access to the entire cylinder volume. Schlieren short-time exposure photographs and high speed movies were used to define the essential features of this flow. The top-land crevice and the regions behind and between the rings consist of volumes connected through the ring gaps. A system model of volumes and orifices was therefore developed and used to predict the flow into and out of the crevice regions between the piston, piston rings and cylinder wall.

High levels of hydrocarbon emissions during light load operation keep the direct injection stratified charge engine from commercial application. Previous analytical work has identified several possible hydrocarbon emissions mechanisms which can result from poor in-cylinder fuel distribution. Poor fuel distribution can be caused by erratic fuel injection. Experiments conducted on a single cylinder DISC engine show a dramatic increase in the cycle to cycle variation in injection characteristics as engine load decreases. This is accompanied by an increase in cycle to cycle variation in combustion behavior suggesting that degradation in combustion results from the degradation in the quality of the injection event. Examination of combustion and injection characteristics on a cycle by cycle basis shows that, at light load, IMEP and heat release do not correlate with the amount of fuel injected into the cylinder.