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The influence of cetane-detergent additives in diesel fuel increased to 10% of RME content on energy parameters and exhaust gas composition of a diesel engine

According to EU preferences, for well-known reasons, the aim is to increase the rapeseed methyl ester (RME) content in the diesel fuel standard. Currently (2019) the mandatory RME add-on to diesel fuel, which is sold at petrol stations in Europe, is 7%. The fuel used in the tests contained 10% of RME. Unfortunately, however, an increase in the amount of methyl esters of vegetable oils is related to i.e. a decrease in the stability of such fuel during storage, increased pollution of the combustion chamber and fuel injector, and increased NOx concentration in the engine exhaust. Then the increase in NOx emissions in the exhaust gases is mainly the result of the influence of RME on the elongation of the self-ignition delay and what is connected with the increase in the combustion dynamics and consequently the maximum combustion temperature. Therefore, to avoid the mentioned negative effects of increasing the amount of RME in the fuel (to 10%), three different additive packages were used: stabilising, washing, and increasing the cetane number with different concentrations. The tests were carried out using a 4-cylinder, turbocharged 1.9 TDI engine from VW. The tests were carried out for 4 fuels (comparative fuel with a content of 7% RME and 3 test fuels with a content of 10% RME, differing in the content of the additive package). For all the fuels, the measurements were carried out at constant engine speed and 6 engine loads. Measured and analysed were, among others: fuel consumption (Gp and ge), overall engine efficiency (o), excess air factor (, temperature (tp), and air pressure (pd) in the intake manifold, exhaust gas temperature before turbine (ts), start of fuel injection (pw), O2, , CO2, CO, NOx concentration and smoke opacity (D) measured before the exhaust gas aftertreatment system (oxidising catalytic converter). It was found that each of the 3 additive packages used does not have a significant impact on fuel consumption and, therefore, on the overall efficiency of the engine. However, a different effect of the tested additives on the composition of exhaust gases was observed. The first package had a slight effect on reducing the NOx concentration in the exhaust, but only for small engine loads. Since NOx emissions are relatively low at these engine loads and the EGR system still works, the use of this additive package seems to be of little interest. On the other hand, the second additive pack worked more effectively only at higher engine loads (in relation to the reduction of NOx concentration in the exhaust gases). In the third packet, the amount of the cetane additive was doubled (compared to the second packet). Then, the reduction in the NOx concentration in the exhaust gas by 3-8% was obtained with reference to the comparative fuel. In order to analyse the cause and effect of the occurrences, the measurements were extended by indicating the engine cylinder and calculating the rate of heat release. The synthesis of the measured parameters has been included in the second article by the authors which was proposed for publication, entitled: "Influence of cetane-detergent additives to diesel fuel with RME content increased to 10% on the parameters of indicator diagrams and rate of heat release in a diesel engine".
Topic: Alternative fuels
Author: Winicjusz STANIK
Co-authors: Jerzy CISEK