Study On The Air Injection Of Bus Turbocharged Diesel Engine

Urban traffic pollution has risen to one of the major sources of China's urban air and noise pollution. As one of the city's main public transport, buses with diesel engine, due to lag of turbocharger response and other reasons, make a sharp increase in harmful exhaust black smoke at the start, acceleration or loading. Therefore, the use of technical measures to improve transient performance and reduce exhaust smoke of the existing diesel buses, not only has great significance, but also a prerequisite to develop public transport.First, the main reasons for the diesel engine smoke were analyzed in this paper, and a comparative analysis of main technical means of reducing smoke was made. Analysis showed that:inlet air injection technical solutions were adopted more easily without the need for damage of the turbocharger structure; it's more suitable for buses. To study the inlet air injection on the improvement of diesel engine smoke and affects of engine's performance and emissions, a test bench based on an electrically controlled turbocharged diesel engine YC6L350-30 was built. Compositions of the test bench were introduced; the basic design of air injection system and its transient measurement and control system to meet the test requirements were described.Secondly, the diesel engine steady and transient experiments for air injection were made respectively, the test conditions of which were determined according to the data of the Wuhan bus road test. The results showed that:(1) In the steady-state operating conditions, air injection improved the engine power, particularly in low-speed and high-load conditions. Meanwhile, the air injection reduced diesel engine exhaust smoke and CO emission. During air injection pressure was maintained at about 3bar, the largest percentage decline of smoke value reached 50%, and the largest percentage decline of CO emission volume concentration reached 60%. However, the improvements of diesel power and emissions were not obvious while injection for those conditions with greater probability during bus running, and the economical efficiency became worse as a result of the injection power consumption. (2) In the transient operating conditions, the greater rate of change of throttle resulted faster smoke rising and higher peak of smoke value. Inlet air injection could effectively reduce diesel engine transient smoke and CO emission. The longer injection time showed a larger decrease in smoke and CO emission. For NOx emission, the emission volume concentration rose in the loading condition, but it was less affected in accelerating conditions while injection. In addition, the effect was better on the improvement of engine performance and emissions while the injection pressure was 3bar; the exhaust smoke and CO emission had a greater decline while injection with double cylinder in loading condition, but NOx emission was increased.In short, in order to solve the smoke issue of diesel engine, this paper presents an inlet air injection solution and makes an experiment study. The results show that:air injection is an effective technology approach, which can significantly reduce exhaust smoke.