Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Full Length Article Evaluation of heat release and combustion analysis in spark ignition Wankel and reciprocating engine Ömer Cihan a, ⁎ , Hüseyin Emre Doğan b , Osman Akın Kutlar b , Abdurrahman Demirci c , Majid Javadzadehkalkhoran b a Hakkari University, Engineering Faculty, Department of Mechanical Engineering, Hakkari, Turkey b Istanbul Technical University, Mechanical Faculty, Department of Mechanical Engineering, Istanbul, Turkey c Karamanoğlu Mehmetbey University, Engineering Faculty, Department of Mechanical Engineering, Karaman, Turkey ARTICLE INFO Keywords: Wankel engine Spark ignition engine Reciprocating engine Combustion Cycle analysis Emissions ABSTRACT In this study, a single-rotor multi side port Wankel research engine and a single cylinder spark ignition (SI) engine having three different type combustion chamber geometry (MR, Cylindrical bowl, Flat) were used. Engine experiments were performed at 2000 rpm, 3 bar and 5 bar bmep (brake mean effective pressure) and stoichio- metric conditions. Combustion analysis was performed for Wankel and a reciprocating SI engine with three types combustion chamber geometries, which are not included in the literature. In the Wankel engine, the maximum pressure value was lower than the reciprocating SI engines and the maximum pressure obtained far away from the TDC. The reason of this is lower burning velocity and combustion progress toward the expansion stroke. Wankel engine's lower burning velocity also reduced the maximum temperature values. The normalized cumulative heat release rate was about 15% higher than the reciprocating SI engine with different combustion chambers. In Wankel engine, NO emissions are 15–45% lower due to the lower combustion temperatures. On the contrary, THC emissions were up to two times higher due to the combustion chamber geometry and absence of squish effect. The MR type combustion chamber has the highest combustion speed and pressure value due to the intense flow and mixture conditions. In the Wankel engine, combustion process is shifted toward the expansion phase, thus resulting to the lower thermal efficiency. In order to improve this process, additional precaution, such as different mixture formation and flow intensification methods in the combustion chamber are required. 1. Introduction Conventional piston engines are mechanisms by which a crank- connecting rod mechanism converts the reciprocating motion to rota- tional motion [1] and although it has developed in many ways since its existence, it has remained the same in structure [2]. As an alternative to the crank-connecting rod mechanism, rotationally moving mechanisms have been developed. These mechanisms are called rotary engines [3]. The Wankel engines, which is a type of rotary engine, operates ac- cording to the four-stroke cycle principle. Only rotor and eccentric shaft act as moving parts in the Wankel engine. Compared to reciprocating piston engine; there is no valve assembly for intake and exhaust pro- cess. The Wankel engine is provided with intake and exhaust ports on the housing or side part [4]. The moving rotor controls the opening and closing times of the ports. The rotor provides rotational motion due to the pressure generated by the burning gases [5]. By the way, the power is transmitted directly to the output shaft. Wankel engines can reach high rotational speeds [6]. In addition, in evaluation of engine parts, it does not have a crank-connecting rod mechanism compared to the re- ciprocating engine, therefore it has a simpler structure and less parts [7]. Other advantages of the Wankel engine can be listed as light weight, lower NO x emissions and more power production than reciprocating engine with same weight. In addition, it operates with lower vibration due to absence of reciprocating masses such as pistons and connecting rods [6,8]. The comparison of Wankel engine and reciprocating engine in terms of working principle is given in Fig. 1. A full rotation movement of the rotor within housing achieves a four cycle of the Wankel engine. The eccentric shaft rotates three times at a full rotation of the rotor. This means that every eccentric shaft revolution corresponds to one four- stroke cycle [3–5]. As can be seen in the Fig. 1, one four-stroke cycle in https://doi.org/10.1016/j.fuel.2019.116479 Received 15 April 2019; Received in revised form 15 August 2019; Accepted 21 October 2019 ⁎ Corresponding author. E-mail address: omercihan@hakkari.edu.tr (Ö. Cihan). Fuel 261 (2020) 116479 Available online 29 October 2019 0016-2361/ © 2019 Elsevier Ltd. All rights reserved. T