Employing DPF And EGR To Simultaneously Control Particulate And NOx Emissions From Diesel Engine

This study presents the exhaust gas recirculation (EGR), coupled with a high-collection efficiency particulate ceramic filter (DPF) to simultaneously control particulate and NOx emissions from diesel engine.Experiments are carried out using 6120 Diesel engine equipped with DPF. The results indicate that the filter's average particulate cleaning efficiency is above 95 percent, the back pressure increases approximate linearly. And the filtration period of single filter is more than 2 hours at 3 BSU soot emission level, therefore two filters working simultaneously can work enough time continuously before the back pressure comes to the certain guideline value. Effect of trapped particulate amounts on the regeneration process is notable. The more the amount of particulates trapped is, the higher the temperature in ceramic during the regeneration process is, but excessive particulates amount will cause melting inside the ceramic. The less the amount of particulates trapped is, the lower the temperature in ceramic during the regeneration process is, but too little particulates amount will cause unstable regeneration process, even stop the regeneration. When the particulates amount is between 23g and 25g, the best regeneration performance can be obtained.By adjusting the distribution of both holes and electric heater components, and adopting double-layer filter, the regeneration performance can be further improved.Based on the porous medium theory, the formula which relates the pressure drop of the wall-flow ceramic and the engine conditions is deduced, the wall-flow ceramic pressure drop depends on two variables, the engine speed and the exhaust gas temperature. The coefficients are determined by disposing experimental data using the linear regression method, then, the pressure drop can be calculated using the formula and the two measured values of engine speed and exhaust gas temperature. The particulates amount on the occasion of regeneration determined by the former formula can be controlled in range of 22gm and 28gm. The key technical problem of how to determine regeneration occasion in the practical application is solved efficiently.The valve used to adjusting the regeneration gas flow is referred to as the regeneration valve. On the basis of fluid mechanics principle, considering the character of the engine, the formula which relates the regeneration valve opening and engine load, the exhaust gas temperature and back pressure is also deduced. Two steps are involved to determine the regeneration valve opening in practical application. First, determine the regeneration valve opening according to standard valve opening MAP. Secondly, correct the regeneration valve opening using the opening correction formula according to experimental load. Thus determined regeneration valve opening realizes the aim that the oxygen flux keeps almost unchangeable during the regeneration process, satisfies the requirement in practical application, and solves the key technical problem of how to determine the exhaust flux in the filter during the regeneration process.Regeneration experiments are carried out at both steady and transient engine operation conditions while the regeneration valve opening is controlled by ECU. The results show that the regeneration temperature distribution is even, the peak temperature in the ceramic centeris controlled under 1000℃, and the radial temperature gradient is under 30℃/cm , the regeneration process is steady, the average regeneration efficiency can reaches above 80 percent, and the regeneration success ratio reaches above 97 percent.A new EGR system, which is based on universal exhaust gas oxygen (UEGO) sensor and controlled by a closed loop, is developed. The system uses the filtered clean recirculation exhaust gas. Using the air-fuel ratio measured by UEGO as the feedback to control EGR,...