Search Results

This paper describes engine research - which supports our program to develop a gasoline engine management system (EMS) with an on-board reformer to provide near-zero tailpipe emissions. With this approach, the reformer converts gasoline (or another hydrocarbon-containing fuel) into reformate, containing hydrogen and CO. Reformate has very wide combustion limits to enable SI engine operation under very dilute conditions (either ultra-lean or with heavy EGR concentrations). In previous publications, we have presented engine dynamometer results showing very low emissions with bottled reformate. This paper shows the sensitivity of engine emissions and performance to operating near the dilute limit with H2 enrichment using both bottled reformate and an actual reformer prototype.

A quick and repeatable test procedure has been developed to investigate cold-start spark plug fouling using a single-cylinder test facility which is capable of quickly cooling the engine back to the test temperature. With a constant engine speed of 140 rpm, the fuel flow is controlled for a 5 minute start/idle period, followed by a 5 minute cool-down period with the fuel off. This facility dramatically reduces the cold-soak period of a cold start which would otherwise require hours. Under conditions where carbon fouling occurs, the effects of fuel calibration, fuel properties (aromaticity, vapor pressure, and surfactant additives), and spark properties (energy and gap size) on the number of cold starts, the spark waveforms, and the electrical-shorting mode were investigated. Fuel calibration had the strongest influence. The relative roles of soot and water and of different soot formation mechanisms are discussed.

Effects of fuel/air equivalence ratio variations (Φ = 1.0±0.02) on engine-out and catalyst-out hydrocarbon (HC) mass and speciated emissions were measured under simulated cold-start conditions in order to suggest ways to optimize the engine-controls-catalyst system for minimum HC mass emissions and specific reactivity. A single-cylinder engine (installed in a temperature-controlled room and using commercial-grade gasoline) is run under controlled steady-state conditions (at 24 °C or -7 °C) which simulate cold starting. Speciated and total hydrocarbon emissions are measured from engine-out exhaust samples and from samples taken after an oven-temperature-controlled catalyst (either a fresh platinum/rhodium production catalyst, a 50,000 mile vehicle-aged catalyst, or a ceramic brick with standard washcoat containing no noble metal). Changes in engine fuel/air equivalence ratio (Φ = 1.0±0.02) have a small effect on engine-out HC mass emissions (± 10 %) and specific reactivity (0 - 2%).

This study describes the effect of spark plug location on NO and HC emissions from a single-cylinder engine with a specially modified combustion chamber. The effects of changes in combustion duration caused either by spark location, dual spark plugs, or charge dilution on NO and HC emissions were also examined. Experiments were run at constant speed, constant load, and mbt spark timing. Nitric oxide emissions were the same with the spark plug located either near the intake or exhaust valve, but were higher with the spark plug midway between the valves or with dual ignition. Hydrocarbon emissions were lowest with the spark plug nearest the exhaust valve and increased with the distance of the spark plug from the exhaust valve. With charge dilution the decrease in NO emission was isolated into a pure dilution effect and a combustion duration effect. The combustion duration effect was minimal at rich mixtures and increased with air-fuel ratio.

Low nitric oxide (NO) emissions and good fuel economy are obtainable at very lean mixtures. However, unstable operation caused by misfire and erratic combustion prevents present spark ignition engines from being operated very lean. A study was undertaken to understand what causes very lean mixtures to misfire in engines. The effects of mixture preparation, intake airflow, exhaust gas recirculation (simulated by N2 dilution), compression ratio, intake mixture temperature, engine speed, number of spark plugs and spark plug locations were investigated at minimum advance for best torque (MBT) spark timing in single-cylinder engines. Propane and isooctane were the fuels used. Results showed that leaner operation was possible with improved mixture preparation, increased airflow, decreased nitrogen (N2) dilution, increased compression ratio, increased mixture temperature, decreased engine speed, more central spark location, and multiple spark plugs.

This study was undertaken to develop a better understanding of how intake charge dilution by various gases affected nitric oxide (NO) emission from a single-cylinder spark ignition engine. Carbon dioxide, nitrogen, helium, argon, steam, and exhaust gas were individually added to the intake charge of a propane-fueled, single-cylinder engine operated at constant speed and load. Nitric oxide emission was reduced in all cases. The gases with higher specific heats gave larger NO reductions. The product of diluent flow rate and specific heat correlated with NO reduction. The effects of diluents on calculated combustion temperature, mbt spark timing, and fuel consumption are also presented and discussed.

A method to stratify the fuel-air mixture along the cylinder axis of engines is described. Axial stratification, with the richest mixture near the top of the combustion chamber and the leanest mixture near the piston top, was obtained by imparting swirl to the intake air and by injecting fuel into the inlet port just before the end of the intake stroke. Axial stratification was developed in both single and multi-cylinder engines over the range of operating conditions tested. A production four-cylinder engine modified to operate with axially-stratified-charge, showed: increased combustion stability and tolerance to dilute mixtures; decreased fuel consumption; similar HC and CO emissions; lower NO emissions and octane requirement when compared with the unmodified engine operated at the same overall equivalence ratio.

The axially stratified-charge (ASC) concept was demonstrated in a compact production car by modifying the engine and developing the required control system and calibration. Two production 1.8 L four-cylinder engines were modified to operate as ASC engines by adding shrouded inlet valves to produce swirl, and by providing timed-sequential port fuel injection. One of these engines was calibrated for minimum fuel consumption in the laboratory using a computer-controlled engine and dynamometer. The second engine was installed in a vehicle equipped with an oxidizing catalyst. A complete control system was developed for this engine to implement the minimum fuel consumption calibration in the vehicle. The fuel economy of the ASC vehicle was six percent better than that of the base vehicle. It had acceptable driveability, and had a 91 Research octane requirement on the fuel.

Statistically designed experiments with a port fuel injected, single-cylinder engine were run to determine the effects of injector-, engine-, and fuel-related variables on exhaust smoke and hydrocarbon (HC) emissions. Among injector-related variables, targeting the fuel spray at the inlet valve centerline toward the valve head resulted in low smoke and HC emissions. These factors apparently help break up the fuel spray and they help subsequent vaporization of the fuel droplets. Among engine-related variables, high coolant temperatures and lean mixtures resulted in less smoke and HC emissions, probably because of better fuel vaporization. Gasolines with aromaticity and 90% point close to the maximum of the ranges of commercial gasolines significantly increased HC and smoke emissions compared with gasolines representing the average or minimum values, of these ranges.

This paper describes recent progress in our program to develop a gasoline-fueled vehicle with an on-board reformer to provide near-zero tailpipe emissions. An on-board reformer converts gasoline (or another hydrocarbon-containing fuel) into reformate, containing hydrogen (H2) and carbon monoxide (CO). Reformate has very wide combustion limits to enable SI engine operation under very dilute conditions (either ultra-lean or with heavy exhaust gas recirculation (EGR) concentrations). In previous publications, we have presented engine dynamometer results showing very low emissions with bottled reformate. This paper shows results from an engine linked to an experimental, fast start-up reformer. We present both performance data for the reformer as well as engine emissions and performance results. Program results continue to show an on-board reforming system to be an attractive option for providing near-zero tailpipe emissions to meet low emission standards.