Quasi-Dimensional Simulation of Downsizing and Inverter Application for Efficient Part Load Operation of Spark Ignition Engine Driven Micro-Cogeneration Systems

Within the context of distributed power generation, small size systems driven by spark ignition engines represent a valid and user-friendly choice, that ensures good fuel flexibility. One issue is that such applications are run at part load for extensive periods, thus lowering fuel economy. Employing an inverter (fitted between the generator and load) allows engine operation within a wide range of crankshaft rotational velocity, therefore improving efficiency. For the purpose of evaluating the benefits of this technology within a co-generation framework, two configurations were modeled by using the GT-Power simulation software. After model calibration based on measurements on a small size engine for two-wheel applications, the downsized version was compared to a larger power unit operated at constant engine speed for a scenario that featured up to 10 kW rated power. Indeed, the downsizing concept was found to ensure an electrical efficiency improvement of around 10% at 50% load, over 30% at 20% load, and reduced fuel consumption by over 50% at lower load. The co-generation potential was also evaluated, and it resulted practically the same from full to 50% load, while at low load the larger engine featured heat recovery potential up to two times larger compared to the smaller unit.