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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.

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.

This paper first reports on the benchmarking of a gasoline- fueled vehicle currently for sale in California that is certified to ULEV standards. Emissions data from this vehicle indicate the improvements necessary over current technology to meet SULEV tailpipe standards. Tests with this vehicle also show emissions levels with current technology under off-cycle conditions representative of real-world use. We then present Delphi's strategy of on-board partial oxidation (POx) reforming with gasoline-fueled, spark-ignition engines. On-board reforming provides a source of hydrogen fuel. Tests were run with bottled gas simulating the output of a POx reformer. Results show that an advanced Engine Management System with a small on-board reformer can provide very low tailpipe emissions both under cold start and warmed-up conditions using relatively small amounts of POx gas. The data cover both normal US Federal Test Procedure (FTP) conditions as well as more extreme, off-cycle operation.

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%).

A unique, temperature controlled, single-cylinder engine test facility was designed and constructed to simulate cold starting of a car engine. The temperature of the coolant, oil, fuel and air used by the engine can be individually controlled to -29°C. Moreover, the engine is enclosed in a temperature controlled insulated chamber. With this facility the conditions that occur in a car engine as it cranks and starts, can be quickly duplicated and maintained for detailed study. The supply equivalence ratio values for starting the engine were determined using either gasoline with port fuel injection or propane as a premixed charge. For gaseous propane, the supply equivalence ratio for starting was nearly constant at all temperatures studied. However, for gasoline the supply equivalence ratio for starting increased as the temperature was lowered. The significance of these findings is discussed.

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.

Statistically designed experiments were run in a single-cylinder engine to understand the reason for the decrease in exhaust mass HC emissions found in the Auto/Oil Program with decreasing 90% distillation temperature (T90) of gasoline. Besides T90, the effects of mixture preparation, equivalence ratio, and ambient temperature on emissions and fuel consumption were measured. HC emissions were higher with PFI than with premixed charge, but decreasing T90 decreased HC emissions with both premixed charge and PFI. Rich mixture and low ambient temperature increased HC emissions. Speciated exhaust HC measurements indicate that incomplete vaporization of heavy components of the gasoline (C8-C10 alkanes, C6-C9 aromatics and alkenes) was responsible for higher HC emissions.

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.

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.

Nitrogen-free and nitrogen-doped fuels were investigated using a single-cylinder, spark-ignition engine, and gasoline and diesel-powered vehicles. The single-cylinder engine experiments showed that only NO (nitric oxide) emissions were affected by nitrogen in the fuel and that the percentage of fuel nitrogen converted to NO (PNCNO) ranged from about 5 to 100. Generally, PNCNO increased when equivalence ratio, concentration of nitrogen in the fuel, engine load, or compression ratio decreased; PNCNO also increased as the level of EGR or engine speed increased, or as spark timing was retarded from MBT. The vehicle experiments showed PNCNO to be substantially higher (∼80-90) in gasoline engines than in a diesel engine (∼35), and that equivalence ratio, fuel-nitrogen concentration and EGR affected PNCNO in a multi-cylinder gasoline engine in the same manner as in the single-cylinder engine.

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.

Single-cylinder spark ignition engine experiments conducted at constant speed, fixed airflow, and using isooctane as the fuel, demonstrated the effects of fuel-air mixture preparation on lean operation. Mixture preparation was changed by varying the time of fuel injection in the induction manifold, near the intake valve port. For comparison, a prevaporized fuel-air mixture was also investigated. Emphasis was placed on determining the effects of mixture preparation on combustion characteristics. Based on the results from this study, the often favored prevaporized mixture of fuel and air may not be the best diet for lean engine operation.

The lack of clearly identified constraints for ignition and flame propagation has hindered understanding the processes which limit lean operation in spark ignition engines. This experimental study explores flame initiation and flame propagation as limits of lean operation in engines. In separate tests conducted in a single-cylinder CFR (cooperative fuel research) engine, the spark timing was either advanced or retarded from MBT* in order to determine the ignition-limit or partial-burn-limit spark timings, respectively. These two limiting spark timings were found to converge at lean mixtures. At the MBT lean misfire limit, the ignition-limit, and the partial-burn-limit spark timing lines converged. Apparently flame initiation as well as flame propagation considerations constrain lean operation. The effects of engine and ignition system-related variables on the ignition and partial-burn limits are presented and discussed.

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 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.

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.

Monochromatic ultraviolet (UV) absorbance, temperature, and pressure histories of unburned gas in a single cylinder CFR engine under motored, fired, and autoignition conditions were recorded on a multichannel magnetic tape recorder. Isooctane, cyclohexane, ethane, n-hexane, n-heptane, 75 octane number (ON), 50 ON, and 25 ON blends of primary reference fuels (PRF) were studied. Under knocking or autoignition conditions a critical absorbance at 2600 A was found, whose magnitude was independent of engine operating variables and dependent only on the knock resistance of the fuel. This absorbance increased rapidly when a certain temperature level was exceeded during the exothermic preflame reactions.