Development of a fuel injection system for an opposed piston two stroke HCCI engine

Abstract: HCCI combustion engines can provide high fuel efficiencies with low NOx emissions compared to SI and CI engines due to their lean combustion, high compression ratios and low combustion temperatures. The disadvantage of HCCI is that it is inherently difficult to control. The need for an optimized fuel injection system is crucial in the design of an HCCI engine to achieve desirable and controllable performance. The aim of this thesis was to develop and optimize the fuel injection system for a 2- stroke, opposed piston gasoline engine thus continuing the development of the engine towards achieving stable HCCI combustion. The engine and the components that make up the fuel supply and injection system characteristics were analyzed using experimental and theoretical methods. The mathematical ideal mass of fuel and point of injection was found (when exhaust ports are closed). Injector delay, mass vs. electrical on-time and voltage sensitivity was found. Deflector designs used to divert the fuel flow laterally along the cylinder were studied and prototypes manufactured and tested. The engine was then run with new settings and deflector and the results analyzed. It was found that an L-cut design gave the best spray properties in this situation. An Lcut design with two internal seals gave the most favorable spray angle and atomization. A mass equation was formed that linked the mass injected to on-time in the ECU with consideration of the varying supply voltage. Using this mass equation and taking into account the delay, an ideal injection point was found. Implementing the new deflector and with improved injection timing, the engine was able to run smoothly with the theoretical mass required for λ=1 at 6000rpm and produce 0.28 kW of power. This was a noticeable improvement over previous engine tests which required more fuel mass for stable combustion. In conclusion, information was gained which allowed improvement of the injection timing and fuel control. The engine was run with much more accurate masses of fuel injected and injection times. The deflector improved atomization and optimized the spray angle. The data gained from the tests and analysis can be implemented into the engines ECU code for automated injection timing and fuel mass. This, coupled with the improved spray profile has aided in the continuing development of the engine towards stable, efficient HCCI combustion.