Potential for Improving HD Diesel Truck Engine Fuel Consumption Using Exhaust Heat Recovery Techniques

Abstract

Increased fuel costs and diminishing petroleum supplies are forcing both governments and industries to reduce engine fuel consumption. Up to now significant improvement has been achieved towards this direction using advanced engine techniques such as downsizing, VVT, advance fuel injection, advanced boosting etc. However the potential for further significant improvement is extremely limited. Despite these advancements diesel engines still reject a considerable amount of fuel chemical energy to the ambience through the exhaust gas. This is approximately 30-40% of the energy supplied by the fuel depending on engine load. If part of this thermal energy is recovered and converted to power it could result to a significant reduction of engine bsfc. To achieve this various techniques are available some of which have been partially tested in the past. Mechanical turbocompounding is considered a base technology which combines the output of a diesel engine with that of an exhaust gas driven turbine located downstream of the turbocharger turbine. Electrical turbocompounding is a similar technique using an efficient turbocharger turbine and a high speed generator mounted on the turbocharger’s shaft. The excess turbine power is converted to electricity. However both techniques can be significantly improved especially using advanced turbocharging components and relevant techniques to control and vary power turbine pressure ratio or exhaust manifold pressure (electric turbocompounding) with operating conditions. Another promising technology is