The combustion chamber of a single-cylinder, direct-injection diesel engine was insulated with ceramic coatings to determine the effect of low heat rejection (LHR) operation on engine performance, emissions, and combustion. The results showed that the LHR engine performance was not improved compared to the baseline cooled engine. In general, the LHR engine had lower thermal efficiency with higher smoke and particulate emissions. The un-burned hydrocarbon (HC) emissions were reduced across the load range and the full load carbon monoxide (CO) increased. The nitrous oxide (NOx) emissions increased at some part-load conditions and were reduced slightly at full loads. The poor LHR engine performance was attributed to degraded combustion characterized by less premixed burning and longer combustion duration compared to the baseline cooled engine.

Insulating the combustion chamber of an internal combustion engine theoretically results in improved thermal efficiency according to_ the Second Law of Thermodynamics. However, in practice it is difficult to realize the improvements in thermal efficiency due to the complex nature of the internal combustion engine and the thermal limitations of current materials and lubrication. Several researchers have reported efficiency gains^»^) and losses^3»'*) in LHR engines. There have -also; been^conflicting- data, published concerning, the, effects of LHR engine operation on •engine emissions and combustion.(3,4,53). The conflicting results are probably due to the infinite number of possible LHR engine configurations, test conditions, and analysis techniques used.

' .'The objective of this investigation is not to end the debate on how LHR engine operation affects engine performance, emissions, and combustion, but simply to add the test results for a specific direct-injected diesel engine to the LHR engine database.

. The experimental results of this investigation were compared with analytical predictions made using Integral Technologies Incorporated's (ITI) IRIS engine model.

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