Mechanism of the Smokeless Rich Diesel Combustion by Reducing Temperature

<div class="htmlview paragraph">Recently, the smokeless rich diesel combustion had been demonstrated [<span class="xref">1</span>]. This can realize smokeless and NOx-less combustion by using a large amount of cooled EGR under a near stoichiometric and even in a rich operating condition. We focus on the effects of reducing diesel combustion temperature on soot reduction. In this paper, the smoke suppression mechanism in the smokeless rich combustion, where the temperature is reduced by higher EGR rate, is analyzed by the following procedure.</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"><span class="li-label">(1)</span><div class="htmlview paragraph">ϕ (equivalence ratio) - T (temperature) map, which shows soot formation tendencies as a function of ϕ and T, was made using zero dimensional calculations with a detailed chemical kinetic model including PAH (polycyclic aromatic hydrocarbons) formation, soot particle nucleation, growth and surface oxidation.</div></li> <li class="list-item"><span class="li-label">(2)</span><div class="htmlview paragraph">The combustion processes of the smokeless and conventional diesel combustion were simulated by the 3D-CFD KIVA2 code.</div></li> <li class="list-item"><span class="li-label">(3)</span><div class="htmlview paragraph">In-cylinder conditions of smokeless and conventional combustion predicted by 3D-CFD were plotted on the ϕ -T map to investigate their behaviors and differences on the map.</div></li> </ol> </div> <div class="htmlview paragraph">The following results were obtained.</div> <div class="htmlview paragraph"> <ol class="list nostyle"> <li class="list-item"><span class="li-label">(a)</span><div class="htmlview paragraph">According to 3D-CFD, there is little difference in mixture formation between the smokeless and conventional combustion. It is calculated that the temperature of the smokeless combustion with higher EGR rate is significantly reduced compared with that of conventional one.</div></li> <li class="list-item"><span class="li-label">(b)</span><div class="htmlview paragraph">The smokeless combustion proceeds so as to avoid soot formation regions on the ϕ -T map in contrast to the conventional one, due to this significant temperature reduction.</div></li> <li class="list-item"><span class="li-label">(c)</span><div class="htmlview paragraph">The smoke suppression is realized by the combustion taking place at temperatures below that needed to form soot. In such lower temperature region, the soot formation itself can be suppressed because the reactions forming soot particles from PAH do not progress even if the rich combustion occurs. This shows the reason why the smokeless rich combustion was realized without regard to the improvement of the mixture formation.</div></li> </ol> </div>