The Effects Of EGR On The Combustion And Emission Characteristics Of Common Rail Diesel Engine

Diesel engines have been widely used because of its excellent power and economy performance and high work reliability. However, with the dramatic increasing of the engine amount it becomes the main pollution source in the urban and harmful to people's health and living environment. The stricter and stricter emission legislations have been constituted due to the rising awareness of environment protection. Therefore, to research and develop low emission engine has great importance to controlling environment pollution. The research focus concentrates to reducing NOx and PM emission control to meet the stricter and stricter emission legislations due to the inherent non-balanced pervading combustion mode of diesel engine. Meanwhile, the paradox between economy performance and emission should also be resolved appropriately.This research which utilizes the CA6DL2-35E3 common-rail diesel engine with the turbocharger and intercool system as the sample subject, has designed the experiment control system and cooler parameters in engine cooling system to meet the experiment needs. By virtue of adjusting VVP45.40-25 temperature control proportion valve supplied by Siemens Company, temperature fluctuation is realized within 3°C, which can be considered as invariable temperature control.Set up the principle EGR system and low-pressure EGR system according to two different trial projects. The adoption of combination in series of line electrical engineering drives with electronics control and ball valve operated by hand can regulate EGR rate inside the the whole scope of work condition; The low-pressure EGR system carries on the back pressure which is used under the condition of valve emulation to install SCR, needing a smaller EGR rate and use of common copper ball valve which needs to control its opening degree by hand. EGR water cooler and confirmation of EGR rate are also introduced.The study of the principle EGR experiment: The influence of EGR rate on the combustion process and emission performance of the engine is analyzed. Study conclusions are as follows:Pressure line inside the cylinder presents a pair of peaks, while it tends to present in single peak with the increment of charges; pressure inside the cylinder is consistent under the same charge with the increment of the EGR rate; the first peak and the second peak are lower with the increment of the EGR rate. Under small charge temperature inside the cylinder lowers with the EGR rate increment before the combustion start order, while after combustion start order the EGR rate increment temperature inside the cylinder rises; Under medium and big charge the temperature fluctuates slightly near combustion start point, while after the center of radiation rate, EGR rate enlarges temperature ascension. Under the same charge, the stagnant ignition period is short under small charge, while the stagnant ignition period short in big charge and in small charge the stagnant ignition period expects to grow with aggrandizement but in great charge variety smaller. With the growth of EGR rate, all the combustion start points are postponed, postponing time is long in small charge, and postponing time is short in medium and big charge. In the meantime, radiation rate presents as single peak, the peak postpones behind then goes up and burning period expects to shorten continuously; In medium and big charge, radiation rate presents as a pair of peaks, medium carries a pair of peaks more obviously, the first peak doesn't obviously increase variety regulation with the EGR rate, the second peak with EGR rate increment but lowers, burning period keeping constant.Under same EGR rate the rate of fuel depletion lowers with the growth of charge. In the same charge the twist square descends with the increment of fuel depletion rate with the increase of EGR rate, with small charge fuel depletion rate and twist square vary slowly, while with big charge they vary quickly. NOx emission lowers with the increment ratio of EGR rate under all charges, among them, the small charge's descending range smaller than the medium and big charge.( NOx emission decreased 31% and 51% respectively under the condition of 1.5%~13% EGR rate of small charge and 4%~11% EGR rate of big charge.) In small charge the smoke opacity degree is almost constant with the increment of the EGR rate, while in medium and large charge the smoke thickness grows at a smaller EGR rate. When the EGR rate is bigger than some critical point, smoke opacity degree grows greatly and quickly. With the increase of the charges, this critical point moves towards the smaller EGR rate, thus this point can be used as the reference point to optimize the EGR rate.Experiment on low-pressure EGR: The research studies the influence on the NOx and the PM emission after introducing a little amount of EGR; meanwhile it studies its influence on the motive and economy of the engine; finally feasibility analysis of the route of combining SCR and EGR can be proposed. Study conclusions are as follows:When EGR rate increases, inside pressure, temperature of the cylinder and the first peak of radiation rate (mainly prepared burnable mixture) all lower, and start and terminal burning point as well as pervasion burning are basically the same to the previous condition.At all rotate speeds and charges, that introducing a little waste gas has very little influence on twist square, while the proportion of the emission of NOx decreases greatly. At all rotate speeds, The smoke opacity degree rises a little under small and medium charge; smoke thickness rises much under the leaving conditions.Euro-ESC13 test cycle,the comparison between the optimized and original engine shows: the result of basic optimization has realized its target. At low EGR rate the economy quality of the engine has a little improvement with NOx descending 24.8% and the PM rising 18.75%. On this basis, that emission of NOx decreasing greatly and PM increasing a little can be realized through exactly controlling EGR rate and optimizing appropriately. Therefore, the route of adding EGR technique to SCR by introducing a little amount of exhaust is viable.