Browsing by Subject "low temperature combustion"
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Item Insights into Conventional and Low Temperature Diesel Combustion Using Combustion Trajectory Prediction Model(2014-04-18) Bittle, Joshua AAttempting to bridge the gap between typical off-line engine simulations and online real-time control strategies a computationally efficient model has been created that predicts the combustion trajectory (path through the ?-T plane). To give an indication of time progression in the combustion event the results are first shown as a function of crank angle, but most discussion is focused on the behavior of the combustion trajectory on the ?-T plane. The conditions investigated here include injection timing sweeps between a conventional and late timing (8? and 0? before top dead center, or bTDC, respectively) as well as full exhaust gas recirculation (EGR) sweeps at both timings. These test conditions highlight how EGR influences the combustion trajectory at different timings ? i.e., showing the typical soot-NOx trade-off and the defeat of this trade-off when low temperature combustion (LTC) is obtained. The major insight gained from this modeling approach is how LTC trajectory is different from conventional case in the ?-T plane. Attempting to understand the differences and hypothesizing about the causes suggests that there is no specific region that is defined as LTC. In fact the LTC trajectory looks very similar to a conventional one with just subtle differences that keep it from moving into the soot formation region. Additionally, the traditional conceptual explanations for diesel combustion are explored relative to how they are illustrated in the combustion trajectory, especially the transition from pre-mixed to mixing controlled combustion. Understanding this behavior in this context aids in explaining the different observations for the LTC modes.Item Investigation into the Emissions and Efficiency of Low Temperature Diesel Combustion(2011-10-21) Knight, Bryan MichaelAs global focus shifts towards the health and conservation of the planet, greater importance is placed upon the hazardous emissions of our fossil fuels, as well as their finite supply. These two areas remain intense topics of research in order to reduce green house gas emissions and increase the fuel efficiency of our vehicles. A particular solution to this problem is the diesel engine, with its inherently fuel-lean combustion, which gives rise to low CO2 production and higher efficiencies than its gasoline counterpart. Diesel engines, however, typically exhibit higher nitrogen oxides (NOx [NOx = NO NO2, where NO is nitric oxide and NO2 is nitrogen dioxide]) and soot. There exists the possibility to simultaneously reduce both emissions with the application of low temperature diesel combustion (LTC). While exhibiting great characteristics in simultaneous reductions in nitrogen oxides and soot, LTC faces challenges with higher carbon monoxide (CO) and hydrocarbon (HC) emissions, as well as penalties in fuel efficiency. The following study examines the characteristics of LTC which contribute to the differences in emissions and efficiency compared to typical conventional diesel combustion. More specifically, key engine parameters which are used to enable LTC, such as EGR and fuel pressure are swept through a full range to determine their effects on each combustion regime. Analysis will focus on comparing both combustion regimes to determine how exhaust gas recirculation (EGR) and fuel pressure relate to lowering NO and smoke concentrations, and how these relate to a penalty in fuel efficiency. This study finds that the application of LTC is able to realize a 99 percent reduction in NO while simultaneously reducing smoke by 17 percent compared to the conventional combustion counterpart. Through a sweep increasing EGR, LTC is able to defeat the typical soot ? NO tradeoff; however, brake fuel conversion efficiency decreases 6.8 percent for LTC, while conventional combustion realizes a 4 percent increase in efficiency. The sweep of increasing fuel pressure confirms typical increases in NO and decreases in smoke for both LTC and conventional combustion; however, brake fuel conversion efficiency increases 2.3 percent for LTC and drops 4 percent for conventional combustion.