Improvement Research On Emission Performance Of Small Excavator Diesel Engines

Diesel engines with low fuel consumption, high efficiency characteristics, have a good economy and dynamics performance. Because of the diesel engine combustion characteristics, NO_X and PM emissions is higher than other kind engines, among them NO_X pollution is the most serious problem. Currently, to meet Euroâ…¢emission regulations of diesel engines, often using exhaust gas recirculation to reduce NO_X emissions. Exhaust Gas Recirculation, referred to as EGR, is one of effective measures to reduce NO_X emissions of internal combustion engine. Internal EGR is the use of intake and exhaust valves with gas phase changes so that the residual gas inside the engine cylinder increased, lowering the maximum combustion temperature and reducing NO_X emissions purposes. Internal EGR has simple structure and low cost but no external connection pipe and the EGR valve and other accessories.This paper presents a bimodal structure of the exhaust cam camshaft. This kind of camshaft makes EGR exhaust cam open the exhaust valve slightly when piston close to the bottom dead center in suction stroke, and then the large vacuum degree will suck the exhaust gas in exhaust pipe into the cylinder, in order to achieve internal EGR. In this paper, AVL FIRE software makes three-dimensional numerical simulations of the whole work process of a diesel engine and study the internal EGR how to influence the intake gas flow field, turbulent kinetic energy distribution, O2 concentration, heat release rate and combustion emissions. At last, we compare eight conditions emission test results under the condition of using internal EGR and non EGR , and verify the bimodal exhaust cam program for improving the performance of diesel engine NO_X emissions, so that, we can provide a reference for low-cost improving emissions performance of diesel engine combustion.The results show that we can reduce the amount of diesel NO_X formation after implementing the internal EGR. Partly because the at end of the intake stroke, the exhaust gas re-introduction of the cylinder, to some extent dilutes the concentration of oxygen cylinder, making the area of oxygen in cylinder is reduced in the combustion process. On the other hand, when the exhaust valve opens at the second time, the gap is very small. The high-speed air flow at the part of valve and valve seat consumes turbulent kinetic energy around the environment, so that, the average turbulent kinetic energy of the gas in cylinder near TDC is reduced, combustion reaction rate is slower, the maximum combustion temperature is reduced, the formation of NO_X is decreased.