A. Mohebbi, S. Jafarmadar, J. Pashae,
Volume 2, Issue 2 (4-2012)
Abstract
Nitrogen oxides (NOx) contribute to a wide range of environmental effects including the formation of acid rain and
destroy ozone layer. In-cylinder high temperature flame and high oxygen concentration are the parameters which affect
the NOx emissions. The EGR system is a very effective way for reducing NOx emission from a diesel engine (via
reduction of these parameters), particularly at the high load of engine operation condition. In this study, the influence
of EGR on diesel engine combustion, NOx/PM emissions, brake specific fuel consumption (BSFC), engine thermal
efficiency, cylinder pressure and heat release rate (HRR) are analyzed and presented. The experiments have been
conducted on a turbocharged DI diesel engine under full load condition at two different injection timings in order to
distinguish and quantify some effects of Hot and Cooled EGR with various rates on the engine parameters.
Experimental results showed that increase of EGR rate has a negative effect on air-fuel ratio. For a premixed
combustion at constant boost pressure, ignition delay is increased leading to retardation of all combustion process, a
low HRR peak and reduce of in-cylinder peak temperature. Using of Hot EGR reduces NOX emissions whereas PM
emissions are increased. The advance of injection timing resulted in the reduction PM while both NOX emissions and
fuel consumption were increased. The use of cooled EGR was more effective compared to the hot EGR. As a result,
the EGR temperature has no significant impact on NOx emissions. With increasing EGR rate, unequal EGR
distribution was increased in inlet port of cylinders while the reducing EGR temperature (cooled EGR) improved its
distribution among the engine cylinders and decreased the EGR cylinder-to-cylinder variations.
J. Zareei, A. Rohani, Wan Mohd,
Volume 8, Issue 1 (3-2018)
Abstract
To improve the engine performance and reduce emissions, factors such as changing ignition and injection timing along with converting of port injection system to direct injection in SI(spark-ignited) engines and hydrogen enrichment to CNG fuel at WOT conditions have a great importance. In this work, which was investigated experimentally (for CNG engine) and theoretically (for combustion Eddy Break-Up model and turbulence model is used) in a single- cylinder four-stroke SI engine at various engine speeds (2000-6000 rpm in 1000 rpm intervals), injection timing (130-210 crank angle(CA) in 50 CA intervals), ignition timing (19-28 CA in 2 degree intervals), 20 bar injection pressure and five hydrogen volume fraction 0% to 50% in the blend of HCNG. The results showed that fuel conversion efficiency, torque and power output were increased, while duration of heat release rate was shortened and found to be advanced. NOx emission was increased with the increase of hydrogen addition in the blend and the lowest NOx was obtained at the lowest speed and retarded ignition timing, hence 19° before top dead center.