Insights into Conventional and Low Temperature Diesel Combustion Using Combustion Trajectory Prediction Model
Abstract
Attempting 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 ϕ-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 ϕ-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 ϕ-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.
Citation
Bittle, Joshua A (2014). Insights into Conventional and Low Temperature Diesel Combustion Using Combustion Trajectory Prediction Model. Doctoral dissertation, Texas A & M University. Available electronically from https : / /hdl .handle .net /1969 .1 /152767.
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