Numerical Investigations on Extended Expansion Engine

A great deal of research has been directed towards understanding the dependence of emissions and fuel economy on the operating and design characteristics of spark-ignition homogeneous-charge engine. Several recent investigations have been concerned with modifying the conventional spark-ignition such that the part load BSFC (brake specific fuel consumption) is decreased. Many of the proposed modifications convert the engine from fixed to variable displacement, i.e., the engine size is varied to suit the vehicle needs. Another possible modification to the conventional engine is to control the load of the engine by controlling the timing of the intake-valve closure rather than by variable-density throttling. This investigation examines the delaying intake valve closing as a method of controlling the engine load without incurring the usual part-load throttling losses. The extended expansion engine (EEE) is an engine with the power output regulated by controlling the crank angle at which the intake valve closes (IVC). As in case of a conventional engine the intake valve opens just prior to and remains open through out the intake stroke of the engine. However, the intake valve also remains open over a portion of the compression stroke while the piston pushes part of the cylinder charge back into the intake manifold and stored in a plenum. A one-way valve is provided to prevent the charge from re-entering the carburetor. After the intake valve closes, the actual compression starts and the expansion and exhaust strokes are similar to those of the conventional engine. The effective cylinder volume determines the trapped cylinder charge and therefore the power output, at the time of the intake valve closing. This paper mainly deals with the numerical studies on single cylinder, four stroke, spark ignition, Extended Expansion Engine extended expansion engine with intake valve closure delayed to produce an expansion ratio that is larger than the compression ratio. The Engine processes are simulated on a computer using thermodynamic and global modeling techniques. Further the concept of lean burn technology is applied to the simulated processes and the engine performance and emission characteristics are studied from the simulated results. Two-zone combustion model is adopted for the analysis of combustion. The model is also associated with sub models for calculating the combustion duration and equilibrium composition of five product species. From this investigations and comparison of results, it is concluded that the simulation work developed predicts the performance and emission characteristics of this engine reasonably well. Therefore it is evident that the developed code can be used with confidence for further parametric studies.