Effects of intake pressure on particle size and number emissions from premixed diesel low-temperature combustion

Abstract

SAGE Publications (UK and US)Desantes Fernández, JM.; Benajes Calvo, JV.; García Oliver, JM.; Kolodziej, CP. (2014). Effects of intake pressure on particle size and number emissions from premixed diesel lowtemperature combustion. ABSTRACTIn this study, ten premixed Diesel Low Temperature Combustion engine operating conditions were chosen based on engine intake pressure (1.2 -1.6 bar), intake oxygen concentration (10%, 11%, and 12%), and injection timing (-24°aTDC in all cases). At each intake oxygen concentration, the effect of intake pressure on combustion parameters and emissions measurements (carbon monoxide, hydrocarbons, nitrogen oxides, particulate matter mass concentration, and particle size distributions) was analyzed. Although increased intake pressure resulted in higher in-cylinder charge air density which improved fuel-air premixing and late-cycle oxidation quality, higher intake pressure also advanced the start of combustion (SOC) and thereby decreased the time available for fuel and air premixing. But even with the decrease in premixing time available before SOC, increased intake pressure caused significant decreases in carbon monoxide, hydrocarbon, particulate matter (PM) mass, and particle number emissions. Particle size distribution measurements allowed greater understanding of how higher intake pressure decreased the PM mass concentrations with respect to particle size. To further investigate the experimental results, a 0D engine heat release code was used to analyze combustion temperatures and a 1D free spray model was used to estimate the relative levels of liquid fuel spray impingement on the piston surface and maximum local equivalence ratio at SOC for each test case. Therefore, though the premixing time was shortened by higher intake pressures, the decreased emissions were understood by combined effects of enhanced fuel and air premixing quality and much improved late-cycle oxidation near the end of combustion.

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“…According to Zeldovich's mechanism [4], the NO x formation increases with high pressure and high temperature of the combustion. However, particle mass emission is in fact decreased significantly with high intake pressure [5].…”

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“…Jayashankara [4] showed that the increase of intake pressure led to shortened combustion duration, decreased maximum heat release rate, increased cumulative heat release, increased NOx and decreased soot emissions. Desantes et al [5] found that increased intake pressure resulted in higher in-cylinder charge air density that improved fuel/air mixing and late-cycle oxidation quality, higher intake pressure also advanced the start of combustion (SOC) and thereby decreased the time available for fuel and air premixing.…”