An experimental investigation on engine speed and cyclic dispersion in an HCCI engine Rahim Ebrahimi a, * , Bernard Desmet b a Department of Agriculture and Machine Mechanics, Shahrekord University, P.O. Box 115, Shahrekord, Iran b Laboratoire de Mécanique et Energétique, Université de Valenciennes et du Hainaut-Cambrésis, Le Mont Houy, 59313 Valenciennes, CEDEX 9, France article info Article history: Received 13 January 2008 Received in revised form 3 September 2009 Accepted 7 April 2010 Available online 20 April 2010 Keywords: Homogeneous charge compression ignition (HCCI) Auto-ignition Cold flame abstract This work presents the results of the experimental study on engine speed and cyclic dispersion in a homogeneous charge compression ignition (HCCI) engine. An engine TD43 is used to carry out the research. The combustion parameters are deduced from heat release rate which obtained from the first principle of thermodynamics during a cycle. The experimental results show that the duration of low tem- perature reaction plays an important role on HCCI combustion, particularly at higher engine speeds. Fur- thermore, cyclic dispersion in an HCCI engine presents, under certain operates conditions, a periodic behavior corresponding to 2 or 3 cycles of the engine. It is concluded that the residual gas of a cycle mod- ifies the three properties (temperature, dilution and composition) of gas in-cylinder at the following cycle. Therefore, gas residual directly affects the course of combustion in an HCCI engine. The knowledge of the duration of the different phases of combustion, as well as conditions in which the periodical appearance of misfire cycles occurs, is useful for the definition of regulation strategies. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction It is more than one century that the basic operation of gasoline and Diesel engines has not been the subject of revolutionary changes. Environmental pollutions and energy limitations make us to replace old combustion method with those which fulfill our new concerns. A promising alternative to combustion in Otto and Diesel engines is the homogeneous charge compression ignition (HCCI) process which requests detailed attention [1]. This engine uses a lean premixed air–fuel mixture that is compressed with high compression ratio, resulting in simultaneous auto-ignition in the whole combustion chamber. Furthermore, theoretically the HCCI process eludes locally lean high temperature regions and rich low temperature regions compared to the combustion process for conventional diesel engine. HCCI is currently under widespread investigation due to its potential to lower NO x and particulate emissions while maintaining high thermal efficiency [2,3]. Since HCCI combustion is achieved through auto-ignition, the chemical kinetics of the fuel/air mixture play a key role in determining var- ious combustion characteristics (e.g. ignition start, burn duration). These effects impact the operating range in which HCCI combus- tion can be employed. The HCCI engine concept has superior po- tential for achieving high part load fuel conversion efficiency. This is due to the combination of small pumping losses, high com- pression ratio and short combustion period. However, there are still challenges associated with the successful operation of HCCI engines. The challenges include the control of ignition and com- bustion phasing, reduction of high HC and CO emissions, cold start and transient response of the HCCI engines, etc. Nonetheless, the fundamental understanding of the combustion process in HCCI en- gines is still limited, and there has been increasing number of re- search papers on HCCI [4–6]. Several potential control methods have been proposed to control the HCCI combustion: varying the rate of exhaust gas recirculation [7], using a variable compression ratio [8], using an addition of promoters (additives reducing igni- tion delay time) [9] or blending low cetane number fuels (such as natural gas and methanol) with high cetane number fuels [10] and using variable valve timing to change the effective compres- sion ratio and/or the amount of hot exhaust gases retained in the cylinder [11]. Many researchers have been directed their studies towards the engine speed and cyclic dispersion in an HCCI engine [12–17]. Iida and Igarashi [12] found that the low temperature auto-ignition process having two heat release peaks in HCCI engine while using n-butane as fuel. With changes in equivalence ratio, engine speed, intake temperature, both low temperature reaction and high tem- perature reaction periods were observed. At certain conditions, only the low temperature reaction or only the high temperature reaction was also found to exist. Kong et al. [13] studied the effect 0016-2361/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.fuel.2010.04.005 * Corresponding author. Tel./fax: +98 381 4424428. E-mail address: Rahim.Ebrahimi@gmail.com (R. Ebrahimi). Fuel 89 (2010) 2149–2156 Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel