Research On A 2-Stroke DISI Heavy Fuel Engine's Performance

For its unsurpassed power-to-weight ratio, low package space and low-maintenance design, and heavy fuel's advantages in usage, transportation and price, the two-stroke spark-ignited heavy fuel engine has a good application value in light aircraft. Traditional two-stroke SI engine exists fuel loss during scavenging process and exhaust process, for its system-dependent disadvantage. And heavy fuel can not easily obtain a good spray characteristic which leads to a limit of heavy fuel engine's application. To maintain the potential of the two-stroke engine, AADI systems are the best solution to improve atomisation and mixture characteristics which can improve the combustion process of heavy fuel. With the use of direct injection technology, it can eliminate or alleviate the fuel short-circuit and improve the engine's fuel economy and HC emission.In this thesis, a two-stroke PFI gasoline engine was modified into an air-assist direct injection heavy fuel engine. Experiments were carried out to study the influence of direct injection timing on the engine performance including the engine's power, fuel economy, exhaust temperature, and cold-start condition. The main work was as follows:(1) Based on AADI technology, modifications were taken on the prototype PFI engine. Designed and manufactured a brand new cylinder head for DI use, parts for air/fuel supply system, etc.And established a engine test bench for experimental research.(2) Conducted a contrast experiment to acquire the scavenging efficiency of the DI engine. And the results showed that the scavenging efficiency of the DI engine nearly stayed as same as the prototype engine's.(3) Established an accurate one-dimension model for the DI engine, and conducted a research on the combustion characteristic of heavy fuel under part load condition which provided theoretical basement for further experiments.(4) Experiments were conducted to research the influence of injection timing on the engine's power, fuel economy and exhaust temperature under different loads. The results showed that with the increase of speed and load, the injection-timing advanced accordingly while the engine achieved best power and fuel economy. And with the injection-timing advanced, the exhaust temperature decreased which ensured the engine work in safe range of temperature. But under light load, the injection-timing hardly influenced the engine's exhaust temperature.(5) Mainly focused on the impact of several specific control parameters for AADI system on the DI heavy fuel's cold-start performance. The results showed that with the fuel injection ratioincreased,the process of cold-start decreased. The injection-end timing had little influence on the engine's cold-start performance, but when the injection-end timing advanced too early, the engine's cold-start performance deteriorated. Large range of ignition advance timing could improve the engine's cold-start performance. And with the increase of the fuel-air ratio during the injection, the engine's cold-start performance improved. An appropriate interval of fuel-air led to a rapid cold-start while too large or little interval of fuel-air deteriorated the cold-start performance.