Environmental Engineering Reference
In-Depth Information
incorporating these advanced combustion approaches represent the greatest
promise for simultaneously reducing fuel consumption and environmentally
harmful exhaust emissions. These novel combustion strategies are enabled by
advanced actuation, sensing and control, specifically
direct, multi-point fuel injection
flexible intake and exhaust valve actuation (i.e., variable valve actuation
(VVA))
real-time, in-cylinder sensing/estimation
real-time feedback control
Here the goal is the in-cylinder reduction of greenhouse gases with simulta-
neous increases in efficiency. In order to develop these strategies the physics of
these new combustion strategies and their dynamic coupling with other com-
ponents on the drivetrain must be well understood. This requires the develop-
ment and implementation of strategies for the modeling and control of novel
combustion strategies, including one particularly promising strategy, residual-
affected LTC, an approach for increasing efficiency and reducing NO
x
emis-
sions in ICEs.
4.1.3 Low Temperature Combustion (LTC)
4.1.3.1 Process and Benefits
LTC exhibits improvements in efficiency of up to 15-20% compared to a
conventional spark ignited (SI) engines, making LTC efficiencies comparable
to diesel engines. LTC strategies essentially reduce the in-cylinder, post com-
bustion temperature by 'homogenizing' the combustion event, leading to 'fla-
meless' combustion. This can be achieved by the compression-induced
combustion of a well-mixed reactant (i.e., fuel and air) and residual (i.e.,
combustion products) mixture. This LTC approach (combustion homogeniza-
tion via compression-induced autoignition of a well-mixed reactant/residual
''charge'') is often referred to as ''premixed charge compression ignition''
(PCCI) or ''homogenous charge compression ignition'' (HCCI). The resulting
reduction in the peak combustion temperature leads to dramatically lower NO
x
levels (in fact, to levels which typically require advanced aftertreatment solu-
tions) compared to conventional SI and diesel strategies. Unlike diesel combus-
tion, the lack of fuel rich regions in LTC results in little or no particulate
emissions, a common issue with diesel strategies. One effective strategy for
achieving LTC is through the reinduction or trapping of residual exhaust gas
via VVA. This methodology of using residual gas is called residual-affected
LTC. The key processes in residual-affected LTC are depicted in Fig. 4.3.
Residual-affected LTC (referred to as justLTCintherestofthechapter)via
exhaust reinduction is achieved by using flexible VVA to hold the intake and
