The Status of Experimental Investigations on Low Heat Rejection Engines

Energy conservation and emissions have become of increasing concern over the past few decades. As automobiles are one of the major sources of energy consumption and urban emissions, engineers concerned are under significant pressure to improve their energy efficiency and reduce exhaust emission levels. While tremendous effort has been devoted in improving performance and reducing emissions of current engines, new technologies are also getting attention. One example is the Low Heat Rejection Engine (LHRE). A technological thrust is currently in progress to develop insulated, low heat rejection engines which exhibit higher thermal efficiency and improved exhaust emissions. The low heat rejection engine concept is not new. For the past two decades many have conducted experiments on low heat rejection engines. Although promising, the results of the experimental investigations have been somewhat mixed. Many have shown that insulation reduces heat transfer but none have shown substantial gains in efficiency, performance and emissions. Some investigators even concluded that insulation increases heat transfer and degrades the performance of the engine. This paper presents a general overview about the previous experimental research efforts into low heat rejection engine concept. This paper explains in detail the engine used, test conditions and constraints, insulation materials used, degree of insulation and results obtained by different researchers in their experimental investigation. The factors that affect thermal efficiency, other performance parameters and exhaust emissions were deduced and their influences discussed.