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Investigation of Diesel Spray Penetration, Vaporization, and Combustion in a Pilot-Ignited Natural Gas Engine, 03-9074

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Principal Investigators
Timothy J. Callahan
Gary D. Bourn

Inclusive Dates: 04/01/98 - Current

Background - Future stationary natural gas engines in the one- to two-megawatt power range are expected to achieve an efficiency of 50 percent and a NOx emissions level of five parts per million. Achieving these goals requires that new technology be developed during the next four to six years. A promising technology for natural gas engines is micropilot prechamber combustion (MPPC). MPPC uses a diesel pilot to ignite a prechamber which, in turn, ignites the natural gas-air mixture in the main combustion chamber. Using this concept permits the ignition of lean air/fuel mixtures required for low emissions and high efficiency. The small pilot quantities and high air velocities in the prechamber create an environment unlike conventional direct-injection diesel engines. However, SwRI must understand the fundamental fuel/air interaction to optimize this combustion system for high efficiency and low emissions.

Approach - High-speed cinematography using the Schlieren technique will be applied to visualize the diesel pilot fuel spray penetration, vaporization, and mixing in an optically accessible prechamber representative of a typical pilot-ignited natural gas engine. A test matrix will be designed to examine the effects of the injection nozzle hole size, fuel jet orientation relative to the air velocity field, and prechamber temperature and pressure. The movies of the injection events will be analyzed for jet penetration and density gradient representing fuel/air mixing. The experimental tests will be simulated using multidimensional modeling. The movies will then be used to validate the computational models by comparing jet penetration data and density gradient fields.

Accomplishments - The optically accessible prechamber and pilot injection system have been designed, procured, and fabricated, and the prechamber has been designed to permit testing with the pilot injector located on either side or the top. The prechamber, quartz windows, window clamps, fuel injector, glow plug, and pressure transducer are shown in the illustration. The prechamber is connected to a pneumatically controlled valve, which controls the admission of heated and pressurized air from a main chamber pressure vessel to simulate the filling that occurs in the engine. An electronic controller is being developed to time the air admission, fuel injection, and imaging equipment. Testing will begin after completion of the test setup, followed by computational modeling and comparison of the results.

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The SwRI-designed prechamber and pilot injection system permits testing with the pilot injector located in three different positions.

Engines, Fuels, Lubricants, and Vehicle Systems Program
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