Environmental Engineering Reference
In-Depth Information
Vigor of Combustion Process
Due to the vigor of the autoignition event, LTC is notably noisier than either of
the conventional IC methodologies. While the uniform nature of the combus-
tion event reduces the peak in-cylinder temperature, and therefore NO
x
, the
rapid rise in in-cylinder pressure elevates the combustion-induced noise. This
necessitates closed-loop control of the combustion timing and evolution to
achieve reductions in the rate of pressure rise.
Solution: Control of the LTC Process
To practically implement residual-affected LTC, closed-loop control must be
used to address the aforementioned challenges.
4.2 Modeling and Control of LTC
4.2.1 History of LTC
The application of LTC to ICEs has been studied since 1979 when it was con-
currently applied to two-stroke engines by Onishi et al. [6] and Noguchi et al. [7]
through use of hot residual gas retained in the cylinder. Since then a large number
of studies of LTC from an experimental and modeling point of view have been
completed. More recently, control of the process has become another focus of the
research community.
In the very earliest experimental work of Onishi et al., several key character-
istics of residual-affected LTC were identified, including the importance of
achieving necessary levels of hot residual to achieve autoignition, uniform
mixing between residual and reactant, and repeatable presence of residual
gases on a cycle-to-cycle basis. In both Onishi et al. and Noguchi et al., the
improvements in efficiency and emissions reduction were identified. The work
of Najt and Foster 1983 [8] outlines the first use of LTC in a 4-stroke engine and
outlines a physical explanation of the process utilizing a simple single-zone
model of the process. Building on the work of Najt and Foster, Thring [9]
examined the use of a gasoline fuel in an LTC engine. In these early works, it
was observed that LTC exhibits some fundamental challenges, including a part-
load limitation and lack of a direct combustion initiator.
4.2.2 Approaches to Modeling LTC
To understand LTC, the dependence of the combustion process on gas
exchange through the intake and exhaust valves, composition of inducted
