Investigation On The Performance Of Turbocompounding System For Internal Combustion Engine Waste Heat Recovery

For internal combustion engine (ICE), only about1/3of fuel energy isconverted into brake power, while most of the other is rejected in exhaust gasesand engine coolant. Waste heat recovery (WHR) is one of key technologies forICE energy saving and emission reduction. Among the various WHRtechnologies, turbocompounding (TC) system recovers exhaust energy usingpower turbine, which is nearest to commercialization because of its simplestructure and low cost. The working process of TC engine is a combined-cycle ofreciprocating ICE and rotating turbine, and thus the match between power turbineand ICE has great influence on engine performance. By now the matching designmainly aims at single operating condition, and the overall performance,especially performance at low engine speed conditions, is not improvedsignificantly. Thus, the performance studies on the match between power turbineand ICE in all operating conditions should be carried out to promote theapplication of TC technology on ICE.A performance simulation model of a heavy-duty diesel engine wasestablished with simulation software GT-POWER, and the model was validatedwith performance experiments data. By adding a power turbine simulation modelto this engine model, a performance simulation platform of TC engine was built,which can be used to study the influence of the match between power turbine andengine turbocharging system on the performance of TC engine in all operatingconditions.In the whole operating conditions, the influence rules of the match betweenpower turbine and engine turbocharging system on the engine performance werestudied under ideal conditions, where efficiencies of power turbine and chargingturbine remained the same with varying conditions. Results show that when airfuel ratio and charging turbine expansion ratio are given, there is an optimalpower turbine expansion ratio where the brake specific fuel consumption (BSFC)is lowest at different engine-speed conditions. The optimal power turbineexpansion ratio increases first and then decreases with increase of chargingturbine expansion ratio, meanwhile it goes up with increase of engine speed. In addition, influence rules of efficiencies of power turbine and charging turbine,engine air fuel ratio and fuel injection advance angle and exhaust valve timingon the optimal matching parameters were also investigated.Based on the law study, three matching schemes between power turbine andturbocharging system were designed, and comparison analysis were carried outamong them. Results show that it is difficult to give consideration to performanceat both high engine-speed conditions and low engine-speed conditions with fixedgeometry turbine, and the matching scheme should be determined based on thecommon use condition of a TC engine. When the scheme is adopted where apower turbine matches with an appropriate VGT turbocharger, the TC engine canperform well at both high and low engine-speed conditions to improve the overallperformance.Based on the VGT and power turbine matching scheme, the heavy-dutydiesel engine was converted into TC engine, and performance experiments arecarried out. Results show that compared with the prototype diesel engine, theBSFC of TC engine decreases under full load within the whole engine-speedrange as much as8.6%.