VOL. 11, NO. 12, JUNE 2016 ISSN 1819-6608 ARPN Journal of Engineering and Applied Sciences © 2006-2016 Asian Research Publishing Network (ARPN). All rights reserved. www.arpnjournals.com 7565 AIR FLOW BEHAVIOUR ON DIFFERENT INTAKE MANIFOLD ANGLES FOR SMALL 4-STROKE PFI RETROFIT KIT SYSTEM Mohd Faisal Hushim 1 , Ahmad Jais Alimin 1 , Mohd Azahari Razali 1 , Akmal Nizam Mohammed 1 , Azwan Sapit 1 , and Julio Cesar Mendez Carvajal 2 1 Automotive Research Group, Centre for Energy and Industrial Environment Studies, Faculty of Mechanical and Manufacturing Engineering, Universiti Tun Hussein Onn Malaysia, Pt. Raja, Batu Pahat, Johor, Malaysia 2 Department of Mechanical Engineering, North Carolina A and T State University, Greensboro, North Carolina, United States of America E-Mail: mdfaisal@uthm.edu.my ABSTRACT Air flow behaviour plays an important role in order to provide better air fuel mixture inside the intake manifold for port fuel injection (PFI) system before it is drawn to the combustion chamber. This paper presents a computational fluid dynamics study that investigates the air flow behaviour inside different intake manifold angles. This study is a continuation from the author’s previous studies that have been conducted by experiment and simulation study using a different simulation tool (GT-POWER). Six angles of intake manifold have been investigated using CFX simulation tool which are 30°, 60°, 90°, 120°, 150°, and 180°. From the study, results indicated 180° as the best option for intake manifold angle due to better air flow behaviour inside the intake manifold. This show an agreement to the previous submitted results that was done by using GT-POWER. Keywords: intake manifold angle, PFI system, air flow behaviour, small 4-Stroke engine. INTRODUCTION This paper is a continuation of the study that investigates the effects of different intake manifold angle of a retrofitted port fuel injection (PFI) system to the small 4-stroke 125 cc engine performance. The authors have studied its effects by experiment and simulation using a different simulation tool (GT-POWER). Based on previous studies , high angle of intake manifold will provide better engine performance in terms of high brake torque (BT), brake power (BP), brake mean effective pressure (BMEP), and volumetric efficiency (VE) (Mohd Faisal Hushim, Ahmad Jais Alimin et al. 2012, Hushim, Alimin et al. 2013). Due to this, a continuation study was done in order to investigate the air flow behaviour inside the intake manifold with different angle. Engine performance and exhaust out emissions for an engine depends on several factors, and one of that is air fuel mixture behaviour. For a PFI system, air and fuel will mixed together inside the intake manifold before it is be drawn to the combustion chamber. The PFI fuelling system is comprised of two major parts which are fuel injector and intake manifold. Fuel injector will inject a certain amount of fuel in the form of fuel mist based on fuel demand commanded by an electronic control unit (ECU) of the system. On the other hand, the intake manifold is a mechanical device that plays an important role to provide good air fuel ratio (AFR) to the spark ignition (SI) engine. The main function of an intake manifold is to deliver as much air-fuel mixture to the combustion chamber as possible. There are several researchers (until now) that are working on either experimental or simulation study to investigate the effect of intake manifold to the performances and exhaust emissions of the internal combustion engine (ICE) (Yasar, Sahin et al. 2006, Al- Rousan and Al-Ajlouni 2008, Iida, Yoshikawa et al. 2009, Ceviz and AkIn 2010, Sulaiman, Murad et al. 2010, Bordjane, Chalet et al. 2011). Ceviz and AkIn (2010) studied the effect of variable length plenum on the performance characteristics of ICE. This is one of the most remarkable developments of intake manifold. From the study, the variation of plenum length causes an improvement on the engine performance characteristics especially in engine specific fuel consumption. Although it proves the positive improvement, however, the design is too complex and expensive to produce. Al-Rousan and Al-Ajlouni (2008) stated that homogenous mixture is important in order to optimize volumetric efficiency, improve fuel economy and reduce exhaust emission because this mixture is easy to evaporate, burn and consumed by the engine. Sulaiman et al. (2010) performed an investigative study on the air flow characteristics in various designs of intake manifold by experiment test and numerical approach. The simulation study was done using computational fluid dynamics (CFD) software - Fluent and the results were validated by experiments approach using a commercial flow bench. Their studies are of interest for this study, because they used a slightly similar test engine characteristic, which are a single cylinder 4-stroke spark ignition engine with one valve each at the intake and exhaust ports. However, the engine’s capacity is 200 cc compared to the current authors research, with the selected engine being only 125 cc. Flow rate and flow coefficient of air entering the combustion chamber are two parameters that are of interest. From the studies, they reported that a different up to 20% in the mass flow rate can be recorded due to the variations in the geometry of intake manifold. The variations of intake manifold that were studied by experiment using flow bench are depicted in Figure-1 below.