SETC2009 2009-32-0026 / 20097026 Experimental Investigation of Performance and Emissions of a Sequential Port Injection Compressed Natural Gas Converted Engine How Heoy Geok, Taib Iskandar Mohamad, Shahrir Abdullah, Yusoff Ali and Azhari Shamsudeen Department of Mechanical and Materials Engineering, National University of Malaysia Copyright © 2009 SAE Japan and Copyright © 2009 SAE International ABSTRACT A single cylinder port injection gasoline engine was converted to a bi-fuel gasoline-compressed natural gas operation. The engine was run at wide open throttle and speeds ranging from 1500 to 5000 rpm. Cylinder pressure and air-fuel flow rate were recorded to calculate the indicated performance. Results show CNG operation yields higher FCE and lower ISFC. However, the indicated power, indicated torque, IMEP and volumetric efficiency of CNG were reduced due to lower charge density and slower flame speed. In terms of exhaust emissions, CNG shows significantly lower emission of HC, CO 2 and CO. The NO x emission however shows mixed behavior. INTRODUCTION The use of alternative fuels in automotive engines has gained more attentions due to the increased conventional fuel prices and enforcement of stringent emission limits. Various alternative fuels suited for spark ignition (SI) engines have been studied extensively and utilized in vehicles. Promising results have been obtained from the fuel economy and exhaust emissions points of view [1-3]. These fuels can be categorized into synthetic gasoline, alcohols and gaseous fuels [4, 5]. Among all, natural gas is probably the most widely studied and used alternative fuel due to its worldwide availability and also its adaptability to the gasoline and diesel engines. Natural gas-fuelled engine has the potential for obtaining higher thermal efficiency, less knocking tendency and low CO 2 exhaust emissions due to its lower carbon-to- hydrogen ratio and higher octane value which allows higher compression ratio operation compared to those of gasoline [6-8]. Nowadays, most natural gas-fuelled engines are converted from gasoline or diesel engine. Only small fractions are developed for dedicated compressed natural gas (CNG) operation. The converted engine uses the built-in fuel system (i.e. carburettor or port injection) to deliver fuel to the cylinder. These result in some drawbacks, mainly reduced power and limited upper speed, which are due to lower charge inhaled energy (due to reduced volumetric efficiency) and slower natural gas flame speed respectively [9]. It is reported that power, volume efficiency and brake mean effective pressure were reduced significantly when converting port injection engine from gasoline to natural gas [10-12]. One method to overcome the problem is to directly inject natural gas into the combustion chamber. Direct injection (DI) can increase the absolute heating value of the cylinder charge and enhance turbulence intensity for better mixing prior to ignition [13]. Combustion efficiency is increased which produces better torque and power, reduces pumping and heat losses and allows better control of the air fuel ratio (AFR) [14-16]. Besides, DI of natural gas can maintain the smoke free operation of SI engines and produce lower NO x emissions compared to the unthrottled diesel engines [17]. However, the development of a DI engine is costly and technically difficult. This is due to the needs for development of a new cylinder head to acclimate with direct fuel injector and also involves tedious calibration of the engine control system [18]. Sequential port or manifold fuel injection of natural gas can offer an immediate solution for the drawbacks of CNG converted engine. In this system, natural gas is injected by an injector at the intake manifold just before the opening of intake valve. As a result, better control of mixture formation and response to changing speed can be achieved by using programmable electronic control unit (ECU). Thus, it provides the opportunity to reduce the negative effects on the performance compared to carburettor-type CNG fuel system. This paper discusses the results obtained from experimental investigation of the sequential port/manifold injection natural gas engine with respect to performance, combustion characteristics and exhaust emissions. EXPERIMENTAL SETUP AND PROCEDURES A single cylinder port injection gasoline engine was converted to a CNG-gasoline bi-fuel sequential port fuel injection and a programmable ECU was installed to control the CNG operation. The engine can be operated either with gasoline or CNG by switching