Effects of Intake Temperature and Equivalence Ratio on HCCI Ignition Timing and Emissions of a 2-Stroke Engine Mohammad Izadi Najafabadi 1,a , Nuraini Abdul Aziz 1,b , Nor Mariah Adam 1,c and Abdul Mutalib Leman 2,d 1 Department of Mechanical and Manufacturing Engineering, Faculty of Engineering, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia. 2 Department of Plant and Automotive Engineering, Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, Batu Pahat, 86400 Johor, Malaysia. a izadi.n@hotmail.com, b nuraini@eng.upm.edu.my, c mariah@eng.upm.edu.my, d mutalib@uthm.edu.my Keywords: HCCI, 2-Stroke Engine, Ignition Timing, Intake Temperature, Equivalence Ratio. Abstract. Homogeneous charge compression ignition (HCCI) combustion, when applied to a gasoline engine, offers the potential for a noticeable improvement in fuel economy and dramatic reductions in NOx emissions. In this study, Computational Fluid Dynamic (CFD) is used coupled with detailed chemical mechanism (38 species and 69 reactions) for simulation of HCCI combustion of iso-octane and transitional flow inside the combustion chamber of a 2-stroke engine. Results show that increasing the overall gas temperature significantly advances the HCCI combustion timing. Concerning the equivalence ratio, by increasing it the ignition timing has been advanced and the maximum cylinder pressure has been increased. When equivalence ratio increases to more than 0.5 , NOx emissions significantly increases and go beyond 1000 [ppm]. Introduction Over the last decade, an alternative combustion technology, commonly known as homogeneous charge compression ignition (HCCI), has emerged that has the potential to decrease emissions and fuel consumption in transportation [1]. An engine concept capable of combining the efficiency of a diesel engine with the emissions levels of an Otto engine is the Homogeneous Charge Compression Ignition (HCCI) engine [2]. HCCI engines run well on lean fuel /air mixture, which lead to lower combustion temperatures favoring low NOx emissions and good thermal efficiency. Due the fuel/air mixture is premixed there are no locally fuel-rich regions that are conducive to soot formation. Lots of research works were performed during 1970s by Souk Hong Jo and his colleagues to study the part load lean 2-stroke combustion [3]. They discovered that the irregularities of the combustion and the auto-ignition which were considered as the weak points of the 2-stroke engine could be effectively controlled. This period was successfully concluded by the work he published with his colleague Onishi who managed to get a part load stable 2-stroke combustion process for lean mixtures in which ignition occurs without spark assistance [4]. Another paper concerning 2-stroke auto-ignition was published in 1979 by Noguchi [5]. He concluded that HCCI combustion occurred similarly without flame front while showing great efficiency and emissions figures. They were the first to suggest that active radicals in residual gases could play an important role in the auto-ignition process. During the second half of the 1980s, Duret tried to apply Onishi’s work to DI 2-stroke engine [6]. The first application of HCCI auto-ignition with direct fuel injection engine was then described in 1990 [7]. This research work was further developed until the mid-1990s and the interest of using transfer port throttling to even better control the degree of mixing between the fresh charge and the hot and reactive residual gas was demonstrated [8]. The lack of data in the field of HCCI 2-stroke engines is more significant in compare with 4-stroke engines because HCCI studies are more concentrated on 4-stroke engines. Also studies done in 2-stroke HCCI engines have commonly based on high Compression Ratios engines. So in this study effects of some parameters on ignition timing and emissions of HCCI combustion are investigated in a “low CR 2-stroke engine” to improve the HCCI knowledge in this area. Applied Mechanics and Materials Vol. 315 (2013) pp 498-502 © (2013) Trans Tech Publications, Switzerland doi:10.4028/www.scientific.net/AMM.315.498 All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of TTP, www.ttp.net. (ID: 202.188.27.15, Universiti of Putra Malaysia, Serdang, Malaysia-04/03/13,12:49:49)