A high efficiency 20 kWe microcogeneration unit based on a turbocharged automotive gas engine

The paper deals with the design and the overall performance of 20 kWe cogeneration plant, suitable for local energy conversion and based on a wide-spread automotive internal combustion engine. The manuscript starts by defining the state of art of commercial cogenerators of the same power, underlining that a higher electric efficiency, which leads to a lower heat to electricity ratio, can elevate the annual service factor and the economic effectiveness while reducing CO2 emission. Then is reported the concept which leaded to the specific choice of a small displacement, high boosted engine (in terms of brake mean effective pressure) made to obtain a significant improvement of the engine global efficiency especially at partial load (if compared to most of the best competitors) and consequently a higher electric efficiency. The unit has been derived from a turbocharged Diesel engine, then converted into a spark ignition methane/natural gas system and finally coupled with an asynchronous liquid cooled generator together with high efficiency heat exchangers and some unconventional heat recovery devices in order to maximize thermal efficiency. The whole system, after being placed into a sealed capsule expressly designed to reduce heat losses and noise emission, has been tested as an electricity/heat generation plant to know its running global behavior.