Laser Ignition in Gasoline Direct Injection Engines, 03-9354Printer Friendly Version
Inclusive Dates: 10/01/02 - Current
Background - The objective of this research is to improve upon the current Gasoline Direct Injection (GDI) engine technology for use in automotive applications. GDI engines use stratified charge, unthrottled operation to achieve improved part-load fuel economy over conventional Port Fuel Injection (PFI) engines. One of the drawbacks of current GDI technology is that the fuel spray dynamics required for proper stratified charge operation usually results in liquid fuel impingement on combustion chamber surfaces. The liquid fuel impingement is used to create a near-stoichiometric fuel/air mixture near the wall-mounted spark plug, but a fuel-lean mixture in the remaining volume of the combustion chamber. However, a portion of the liquid fuel remains on the chamber surface and does not participate in the combustion process, resulting in high levels of unburned hydrocarbon emissions and less-than-optimal fuel economy. The premise of this project is that a laser ignition system can replace the wall-mounted spark plug and ignite the mixture at a location away from the chamber walls, negating the need for intentional fuel/wall interaction. This approach is expected to result in improved fuel economy and emissions.
Approach - An existing spark-ignited PFI research engine will be modified for installation of the GDI system, including the fuel injector and the laser ignition system. A 350 mJ pulsed Nd:YAG laser will be used in conjunction with an optical system to transmit and focus the laser beam to the desired ignition location within the combustion chamber. A cylinder head outfitted with a fused silica window will be used to provide optical access into the combustion chamber. Initial testing will utilize a hollow cone-style fuel injector from a leading supplier of fuel system components. A SwRI Rapid Prototyping Electronic Control System (RPECS) will be used to control the laser and fuel injector. The variables that will be studied include the fuel spray pattern, the laser focal point and timing, the details of the optical system, and the engine operating condition. Real-time cylinder pressure and heat release rate data will be combined with emissions measurements to evaluate the performance of the engine.
Accomplishments - A specialized cylinder head with optical access was designed and manufactured for the test engine. The head was manufactured using the Selective Laser Sintering (SLS) rapid-prototyping facility in the Applied Physics Division. The RPECS engine management system was programmed to synchronize the laser Q-switching to the engine. The optical system has been designed, and bench-top testing of the optical system has begun. The engine test stand is currently being fabricated, and incorporates both an AC drive motor and DC generator for motoring and power absorption capabilities.