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In this study, the potential of controlling engine cooling temperature has been investigated experimentally to reduce NOx emissions in heavy diesel engines. Experiments have been done on 90°C and 70°C cooling temperatures that lower temperature obtained via larger radiator and setting its thermostatic valve. Also, the effects of injection timing and the percentage cooled EGR simultaneously have been studied in order to trade-off NOx reduction and increasing other pollutants such as Soot, CO, HC and fuel economy. Experimental results which related to amount of pollutants and fuel consumption by altering the engine cooling temperature, injection timing, and the percentage of cold EGR shows that NOx emissions reduce 17% averagely also fuel consumption decreases negligible.

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The low temperature combustion (LTC) concept is the groundwork of most recent developments in internal combustion diesel engines in order to match stringent environmental standards and regulations. Although, its basic definition which means reducing the combustion chamber temperature to decrease the emissions sounds easy but practical achievement of LTC strategies which can be feasible in a wide range of loads and speeds has its own difficulties. With attention to different effective parameters in a diesel engine combustion process, various methods have been introduced for the purpose of LTC achievement. Two important types of these methods are based upon early and late injection strategies. In addition to analyzing the both mechanisms, in this paper we are intended to implement two different methods in national light duty diesel engine in order to match EURO VI emission standard. One method named UNIBUS is based upon early injection strategies which is benefited from PPC merits and the other one is Modulated Kinetic (MK) which is based upon late injection strategies. Finally both these methods have been compared and contrasted. The results admit the great potentiality of both methods to make a significant and simultaneous reduction in NOx and Soot emissions.