Nigerian Journal of Engineering, Vol. 28, No. 3, December 2021, ISSN (print): 0794 – 4756, ISSN(online):2705-3954. Nigerian Journal of Engineering, Faculty of Engineering, Ahmadu Bello University, Zaria, Nigeria journal homepage: www.njeabu.com.ng Comparative Analysis of Four Stroke and Six Stroke Internal Combustion Renault Engine Efficiency Using Matlab Simulation Tool I. B. Owunna 1 , A. E. Ikpe 2 1,2 Department of Mechanical Engineering, University of Benin, Benin – Nigeria. 1 aniekan.ikpe@eng.uniben.edu Research Article Abstract This study presents a four stroke and six-stroke comparative analysis of Internal Combustion (IC) Renault engine (Mercedes- Benz 250SE, W108 model) efficiency using MATLAB 2018b simulation tool. Using air (working fluid) as charge introduced in the four-stroke engine, efficiency of 36.6% was achieved. However, using air as the charge introduced with a recompression stroke occurring at the fourth stroke, efficiency of 43.2% was obtained. Using air as the charge introduced with an exhaust stroke occurring at the fourth stroke, efficiency of 48.4% was obtained. Using water as the charge introduced with a recompression stroke occurring at the fourth stroke, efficiency of 44.6% was obtained. Using water as the charge introduced with an exhaust stroke occurring at the fourth stroke, efficiency of 51.5% was obtained. The results indicated that six-stroke engine has a higher efficiency than four stroke IC engine when air is used as working fluid while the efficiency of six stroke IC engine is higher when water is used as working fluid compared to when air is used. Copyright © Faculty of Engineering, Ahmadu Bello University, Zaria, Nigeria. Keywords Article History Efficiency; Internal combustion; Six Stroke; Four stroke; Renault engine Received: – April, 2021 Reviewed: – July, 2021 Accepted: – November, 2021 Published: – December, 2021 1. Introduction Internal combustion (IC) engine is a type of engine in which the combustion in the combustion chamber occurs internally. The combustion of air-fuel mixture in IC engine occurs in the combustion chamber of the engine where heat generated in the process reacts with the air-fuel mixture to form hot gases, thereby increasing the internal pressure within the engine cylinder (Ikpe et al., 2016a; Ikpe et al., 2016b). The in-cylinder pressurised air-fuel mixture gradually builds momentum at increasing temperature starting from 293.92K. This causes reciprocating movement of the piston which is translated to the rotating motion of the crankshaft (Lewis, 2013; Soda, 2013). In the process of the reciprocating piston transferring force from expanding gas in the cylinder to the crankshaft through the piston rod and/or connecting rod, mechanical work is achieved (Owunna and Ikpe, 2020). After each compression cycle, the IC engine undergo combustion followed by the expansion of the compressed air-fuel mixture in the cylinder. Internal combustion engines have undergone several improvements in recent times, which have led to significant advantages in the engine operating cycle such as relatively low initial cost, high power density and efficiency as well as the ability to meet emission standards (Caton, 2018; Ikpe and Owunna, 2020). Internal combustion engines consist of various types which includes: Two stroke engine, the four-stroke engine and the six stroke engine. Examples of I.C engines includes; Scram jet engines, Wankel engine, Rocket engines, Pulse Jet engines, Ram Jet engines, Turbojet engines, Turboprop engines, Turbofan engines, Turbo shaft engines etc. In the World today, four stroke cycle engine is widely used in cars, heavy duty vehicles as well as heavy duty machines, etc. These engines consume fuel on a daily basis whose value may stretch largely annually and as much has effect on the fuel economy. Apart from the effect on the economy, exhaust gases released from such engines into the environment causes pollution and also aid in the depletion of the ozone layer by the release of greenhouse gases. Improving efficiency of this engine is something that is highly needed. The six-stroke design was developed by Bruce crower, a veteran of the racing industry and the owner of a company which produces high performance cams and other engine parts. However, four-stroke spark ignition (SI) engine was developed by Nikolaou's Ottoin in 1876 (Mashkour and Ahmed, 2017). Six stroke engine introduces two more strokes which is the fifth and the sixth stroke making it two power strokes and two exhaust strokes. The working fluid of this remaining two stroke being water, makes effective use of the heat energy from the fourth stroke to superheat the water to steam. Due to the addition of two extra strokes, the fuel injection takes place every sixth stroke as compared to every fourth stroke in the original four stroke IC engine cycle (Balse et al., 2015). Therefore, fuel consumption is reduced drastically by more than 40% which may have large significance on the economy as the working fluid is not just fuel alone but water as well which is readily available and cheap (Chaulkar, 2018). A cycle of four-stroke engines is completed by two crankshaft revolutions, while a cycle of six-stroke engines is completed on three crankshaft revolutions (İçingür & Arabaci, 2013). According to Arabaci (2019), one cycle is completed in two revolutions for four- stroke engines, while one cycle is completed in three revolutions for six-stroke engines. This results in lower fuel consumption for the six-stroke engine with the same engine volume. Compared to four stroke engine, six stroke engine has thermal efficiency reaching 50% (30% for the actual internal combustion engines), fuel consumption reduced by more than 62