Control of harmful
pollutants such as oxides of nitrogen (NOx),
particulate matter (PM)/ soot, carbon monoxide (CO), and hydrocarbons
(HC) emitted by diesel engines is essential in order to protect the
environment and human health. Different versions of low temperature
combustion (LTC) concepts have shown their potential in controlling
these pollutants, while achieving thermal efficiencies similar to
conventional compression ignition (CI) engines. In this study, a diesel
fueled partially premixed homogeneous charge compression ignition
(PHCCI) engine was investigated to explore the feasibility of LTC
combustion. All experiments were performed on a constant speed two
cylinder engine prototype, in which one cylinder was modified to operate
in PHCCI combustion mode and the other cylinder operated in conventional
CI combustion mode. An external mixing device, called a “fuel
vaporizer”, was developed for partially homogeneous fuel-air
mixing. For a better understanding of the effect of intake charge
temperature (T
i) and exhaust gas recirculation
(EGR), experiments were performed at three different T
i’s (160, 180, and 200 °C) and three different
EGR rates (0, 10, and 20%) at six engine loads with a relative fuel-air
ratio (λ) ranging from 1.5 (rich limit) to 5.25 (lean limit).
Experimental results showed that fuel-air mixing was significantly
affected by T
i. At higher engine loads,
higher heat release rate (HRR) of PHCCI combustion led to excessive
knocking. Combustion phasing was found to be the most important parameter
in PHCCI combustion, which affected combustion, performance, and emission
characteristics. Increasing T
i improved
fuel-air mixing, leading to superior combustion as well as lower HC
and CO emissions. However, at 200 °C, excessive knocking deteriorated
PHCCI engine performance and led to higher NOx emissions. Increasing
the EGR rate effectively controlled PHCCI combustion, leading to lower
HRR and NOx emissions. However, too high EGR rate increased the CO,
HC, and PM emissions, primarily due to relatively lower combustion
chamber temperatures. This study showed that selection of suitable
control parameters (such as T
i and EGR
rate) led to superior PHCCI combustion, which could possibly extend
the operating load range and engine operating window and may be useful
in developing a practical and efficient LTC engine.