Researches On Reducing Transient Smoke Emissions Of The Turbocharged Diesel Engine With An Electric Supercharger

Turbocharged diesel engines are now widely used on the bus for their high fuel economy, good performance, and high thermal efficiency. It is well known that turbocharged diesel engines suffer from a turbo lag during a sudden load increase, especially at low engine speeds, resulting in insufficient power and high smoke emissions. This undoubtedly do harm to our living environment and physical health.To solve the problem, our team invented an electic superchager, and successfully used it on a naturally aspirated diesel engine. The transient response and transient smoke intensity of the engine were modified. While, in this paper, the electic superchager is used to improve the transient response and smoke intensity of an inter-cooled turbocharged diesel engine caused by turbo lag when suddenly accelerating or loading.To achieve the goal, the electric supercharger should not only reduce freedom acceleration smoke intensity, but also can reduce the smoke intensity at constant load acceleration and constant speed loading of the engine. At the same time it will not bring in negative effects on the engine power while at heavy load. Hence, a tow-staged supercharging system, consisting of two electric-driven compressors and a check valve, is built. It can be used to study the match characteristic between electric-driven compressor and exhaust-driven turbocharger conveniently by measuring mass flow rates of the three cross sections with thermal gas mass flow meter, analyzing velocity field in pressurization gas path between two stages by Particle Image Velocimetry(PIV) technique and investigating change law of flow velocity at the center of the outlet by hot-wire anemometer.Through a series of experimental studies, factors, affecting the fill gas efficiency of the engine, are figured out, the matching method between electric supercharger and turbocharged diesel engine is obtained, and the design principle of the connecting gas path between them is achieved. Eventually, an installation method is determined: an electric supercharger with a 90 mm impeller diameter is installed in parallel with a bypass pipe with a check valve in it and in series with the turbocharger. With this method, the transient smoke intensity of the turbocharged diesel engine(including transient smoke intensity of constant load acceleration and constant speed loading) is reduced.Bench experiment and road test results show that: with the installation method, the free acceleration smoke intensity of the turbocharged diesel engine is reduced from 2.2m-1 to 1.4m-1, and constant load acceleration from 3.5m-1 to 2.4m-1. In addition, if the electric supercharger can be started earlier than the time when the accelerator pedal is pushed, free accelerate smoke intensity can be reduced from 2.2m-1 to 1.1m-1, and the constant load acceleration can be reduced from 3.5m-1 to 1.9m-1.