Low Pressure EGR Calibration Strategies for Reliable Diesel Particulate Filter Regeneration on HDD Engines

Abstract

<div class="htmlview paragraph">Low pressure Exhaust Gas Re-circulation (EGR) can be used along with Diesel Particulate Filter (DPF) systems to reduce NO<sub>x</sub> emissions from heavy-duty diesel engines. Normally the use of EGR decreases NO<sub>x</sub> emissions and increases soot emissions.</div> <div class="htmlview paragraph">The effect of low pressure EGR on DPF regeneration has been investigated in connection with two passive DPF systems. One system contained a catalyst followed by an uncatalyzed DPF and one system was a Catalyzed DPF (CDPF). The objective was to obtain a better understanding of soot oxidation and to develop EGR calibration strategies that would ensure reliable DPF regeneration.</div> <div class="htmlview paragraph">Formation of NO<sub>2</sub> and the subsequent reaction of NO<sub>2</sub> with soot in the DPF, was studied as a function of temperature, EGR rate, and exhaust gas flow rate under steady state conditions for a range of DPF soot preloads.</div> <div class="htmlview paragraph">For the catalyst plus uncatalyzed DPF, NO<sub>2</sub> emissions after the catalyst reached their highest levels at intermediate loads. Soot oxidation started at 200 °C and the rate increased exponentially with temperature. The reaction 2NO<sub>2</sub>+C→CO<sub>2</sub>+2NO prevailed over the reaction NO<sub>2</sub>+C→CO+NO. The influence of NO<sub>2</sub> concentration on soot oxidation became greater as temperatures increased. Soot oxidation rate was directly proportional to soot loading.</div> <div class="htmlview paragraph">For the CDPF, soot loading had only a minor effect on gaseous activity. Soot oxidation rates at different temperatures were similar for the two systems. The CDPF was less dependent on changes in soot loadings and NO<sub>x</sub> concentrations.</div> <div class="htmlview paragraph">The results obtained were used to predict the effects of insulating the exhaust pipe, catalyst size, DPF size, and different EGR rates. EGR calibration strategies for passive DPF systems will be limited by the engine-out soot emissions and engine NO<sub>x</sub>/soot trade-off.</div>