TITLE:
Modeling the Effect of Variable Timing of the Exhaust Valves on SI Engine Emissions for Greener Vehicles
AUTHORS:
Osama H. M. Ghazal, Yousef S. H. Najjar, Kutaeba J. M. Al-Khishali
KEYWORDS:
Variable Exhaust Valve Timing; Spark Ignition Engines; Performance; Emissions; Green Vehicles
JOURNAL NAME:
Energy and Power Engineering,
Vol.5 No.3,
May
7,
2013
ABSTRACT:
The problem with fixed valve timing that the valve train is set by
the automaker for peak efficiency running at a specific point in the engine’s
operating range. When the vehicle is moving slower or faster than this ideal
operating point the engine’s combustion cycle fails to properly burn the
air/fuel mixture leading to considerably compromised engine performance
and wastes fuel. Variable Valve Timing (VVT) is a solution developed to
overcome this engine deficiency, dynamically altering the valve's opening and
closing for optimal performance at any speed. The intension in this work is to
contribute towards pursuing the development of variable valve timing (VVT)
for improving the engine performance. This investigation covers the effect of exhaust
valve opening (EVO), and closing (EVC) angle on engine
performance and emissions. The aim is to optimize engine power and brake
specific fuel consumption (BSFC) where the effect of engine speed has also been
considered. Power, BMEP, BSFC, NO, and CO were calculated and presented
to show the effect of varying valve timing on them for all the valve timing
cases. The calculations of engine performance were carried out using the
simulation and analysis engineering software: LOTUS”, and engine
emissions were calculated using “ZINOX” program. Sensitivity analysis shows
that the reduction of 10% of (EVO) angle gave a reduction of around 2.5%
in power and volumetric efficiency, also a slight increase in nitrogen oxide (NO)
and carbon monoxide (CO), while a 10% decrease in (EVC) causes
around 1% improvement in Power. The effects of different (VVT) from the
simulations are analyzed and compared with those in the reviewed literature.