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A study has been initiated to understand the influence of coolant temperature on HC emissions employing a dual system cooling the cylinder head independently from the engine block. Especially, we have studied its influence on post-oxidation, fuel absorption-desorption, crevice volumes and fuel-air mixture preparation. The results show that the cylinder head temperature has more influence on HC emissions than the block temperature. It was also found that mixture preparation, absorption/desorption and crevice volumes with commercial gasoline is greatly improved by the cooling temperature. The post-oxidation process is also reduced for a decrease of the coolant temperature from 90°C to 35°C.

A light duty truck with a naturally aspirated engine was equipped with a DPF (changing the exhaust pipe and eliminating the muffler) and operated on fuel doped with a cerium based additive in various concentrations. Tests were carried out on chassis dynamometer using the European urban cycle, but also under city driving conditions with maximum speeds up to 50 km/h and exhaust gas temperature up to 300°C. Under these conditions, it was observed that filter regeneration was always possible at relatively high particulate accumulation in the filter, while the effect on fuel consumption (as measured over the emission test cycles) was not detectable, compared to baseline data of the vehicle. Change in driving conditions from slow urban to highway with highly loaded trap led to spontaneous trap regeneration at higher temperatures, without effect on fuel consumption. This paper documents the operation of a fully passive DPF system for diesel light duty vehicles.

A light duty truck Renault Trafic with a naturally aspirated 2.5 l engine was equipped with ceramic DPFs of different sizes, installed at different positions along the exhaust line of the vehicle. The filters were operated on diesel fuel doped with a cerium based additive at concentration of 100 ppm in the fuel. Tests were carried out on chassis dynamometer using the urban part of the new European driving cycle and the full new European Driving cycle. Comparisons are made between the different sizes and positioning as regards both back-pressure build-up and catalytic regeneration behavior. The results show that filter regeneration was always possible at continuous low speed driving, at relatively high filter back-pressure levels (i.e. high particulate accumulation in the filter), with an effect on fuel consumption.