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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.

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.

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.

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.

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.

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.

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.

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.