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Effect of Fuel Injection Strategies and Air Motion in a Medium-to-Heavy Duty, Direct-Injected, Spark-Ignited, Gasoline-Fueled Engine, 03-9024 Printer Friendly VersionPrincipal Investigators Inclusive Dates: 04/01/97 - 07/01/99 Background - In comparison with conventional port-injection engines, direct-injected, spark-ignition (DISI) engines offer the potential for improved performance and fuel economy. In DISI engines, the interaction between the fuel spray and in-cylinder air motion plays a crucial role in the mixture preparation process, which, in turn, has a profound impact on the engine’s performance and emissions characteristics. Two distinct operation modes are used in modern DISI engines, depending on the desired load: 1) a stratified charge is generated by injecting fuel late during the compression stroke and is used at low engine loads, and 2) a homogeneous charge is generated by injecting fuel during the intake stroke and is utilized at medium to high engine loads. Stratified-charge operation offers the greatest potential improvement in fuel economy, but it is also the most challenging to implement successfully. Approach - This project has concentrated on studying the stratified-charge (or late-injection) operating mode mixture preparation process in a medium-duty DISI engine. This goal was accomplished via a two-pronged approach: 1 ) droplet size measurements in a high-pressure chamber were used to characterize the fuel spray from commercial DI injectors under engine-like conditions, and 2) a prototype medium-duty DISI engine was developed to study the effect of injection and spark timing on performance and emissions behavior. Detailed knowledge of the spray characteristics (that is, droplet size, velocity, and distribution in space) under engine-like conditions is instrumental in understanding the fuel vaporization and mixture preparation processes. Experimentation with a prototype medium-duty DISI engine is crucial to quantifying the potential benefits attainable with such engines and in identifying those areas requiring further research. Accomplishments - During this project, several significant accomplishments have resulted. Two commercial gasoline fuel injectors with spray cone angles of 40 and 60 degrees were tested in a high ambient pressure flow facility. Results of this work demonstrate that fuel droplets increase in size at elevated ambient pressures, which helps explain why retarded injection timings (into higher cylinder pressures) result in decreased fuel vaporization. A prototype DISI engine was designed and fabricated using a commercial diesel engine as a base. This engine was successfully operated in stratified charge mode, at air/fuel ratios down to 35/1. Results from this work suggest that efficiency improvements of 20 to 30 percent may be obtained at low engine loads by operating a gasoline engine in stratified charge mode.
Measured fuel spray characteristic droplet size versus ambient pressure.
Computer rendering of the cylinder head modifications for DISI operation. Engines, Fuels,
Lubricants, and Vehicle Systems Program |
