Investigation of a Multicylinder, High-Efficiency, High-BMEP, Heavy-Duty Gasoline Engine Concept, 03-9386

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Principal Investigators
Terrence Alger
Charles E. Roberts Jr.

Inclusive Dates: 04/01/03 - 07/01/04

Background - The motivation behind the development of a heavy-duty gasoline engine is the Environmental Protection Agency's development of increasingly stringent emission standards for heavy-duty diesel engines. These new standards are not achievable through engine tuning alone and necessitate the use of expensive aftertreatment systems. In addition, the presence of the aftertreatment systems and the engine tuning required to make them function serve to reduce the diesel engine efficiency to the point where a high-efficiency gasoline engine may be competitive. Preliminary work on a single-cylinder, heavy-duty gasoline engine indicated that, when equipped with a three-way catalyst, a gasoline engine could compete with a diesel in terms of emissions, efficiency, and cost.

Approach - The proposed approach is to convert an existing diesel engine to run on gasoline. The engine will be retrofitted with a port fuel injection system and a high-energy ignition system. Testing will be conducted at three compression ratios (17.5, 15, and 12.5:1) and two fuel octane numbers (91 and 103) to investigate the load range and sensitivity of the engine to Exhaust Gas Recirculation (EGR), ignition timing, and fuel type. At each compression ratio, a series of constant load sweeps of each variable (EGR percent, ignition timing) will be performed. High-speed in-cylinder pressure data will be acquired along with other engine performance data. The engine will be evaluated for brake thermal efficiency and emissions. The high-speed data will be used to investigate the nature of the combustion process through heat release and percent mass burn curves.

The study will also serve as a feasibility study for the high-efficiency gasoline engine concept. Unknown areas concern the appropriate type of ignition system and the sensitivity of the engine to EGR composition and exhaust backpressure. With the insight gained through this investigation, further work in this area can be planned more efficiently. The lessons learned through this investigation will also constitute a rudimentary design guide for future work in constructing a prototype high-efficiency gasoline engine.

Accomplishments - Testing at a 17.5:1 and 12.5:1 compression ratio was completed using a variety of fuels and EGR/boost combinations. The results show that the engine-out emissions of NOX were two orders of magnitude lower than the baseline diesel. In addition, the fuel consumption of the gasoline engine was equivalent to or, at some operating conditions, less than the baseline diesel engine. This preliminary work indicated that the new combustion technology developed at SwRI can meet 2007 standards for diesel engines with very little aftertreatment for a substantial cost savings at equivalent fuel economy values.

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