Influence of water-diesel fuel emulsions and EGR on combustion and exhaust emissions of heavy duty DI-diesel engines equipped with common-rail injection system

In this paper we investigate the effect of the introduction of water in the combustion chamber of a DI-diesel engine on combustion characteristics and pollutant formation, by using water-diesel fuel emulsions with three distinct water amounts (13%, 21% and 30%). For the measurements we use a modern 4-cylinder DI-diesel engine with high-pressure common rail fuel injection and EGR system. The engine investigations are conducted at constant speed in different operating points of the engine map with wide variations of injection setting parameters and EGR rate. The main concern refers to the interpretation of both measured values and relevant thermodynamic variables, which are computed with analytical instruments (heat release rate, ignition delay, reciprocal characteristic mixing time, etc). The analysis of the measured and computed data shows clear trends and detailed evaluations on the behavior of water-diesel fuel emulsions in the engine process are possible. Accurate measurements of particulate number concentration in the exhaust gas complete the work. At constant injection pressure the reductions of NOx and PM achieved with the 30% water emulsion compared to diesel fuel are about 30% and 70% respectively. These reductions are in all cases proportional to the water content in the fuel. This was measured in all engine load conditions. Due to the fact that EGR lowers NOx and increases particulates but water injection lowers both, there is more flexibility when operating with water-diesel fuel emulsions. With the use of water-diesel emulsions combined with high degrees of EGR and high injection pressures, NOx emissions below 1.0 g/kWh and PM emissions of about 0.01 g/kWh were realized at low load condition without appreciable changes in fuel consumption.

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