An experimental investigation of high performance natural gas engine with direct injection M.A. Kalam * , H.H. Masjuki Department of Mechanical Engineering, University of Malaya, 50603 Kuala Lumpur, Malaysia article info Article history: Received 29 July 2010 Received in revised form 18 February 2011 Accepted 23 March 2011 Available online 22 April 2011 Keywords: DI Engine CNG-BI engine Power SFC Emissions abstract This paper presents experimental results of a new compressed natural gas direct injection (CNG-DI) engine that has been developed from modification of a multi cylinder gasoline port injection (PI) engine. The original gasoline-PI engine was also modified to a CNG bi-fuel system. The test results obtained from CNG fuel using two different systems (i.e. bi-fuel and DI) have been investigated and compared with the original gasoline engine. The objective of this investigation is to compare the test results between CNG-DI, with CNG-BI and gasoline-PI engines with the same displacement volume. It was found that the CNG-DI engine produces similar brake power at 6000 rpm and wide open throttle (WOT) but produces higher brake power at part load condition as compared to the original gasoline. The CNG-BI engine produces 23% lower brake power than the CNG-DI engine. The average brake specific fuel consumption (BSFC) of the CNG-DI engine was 0.28% and 8% lower than gasoline-PI and CNG-BI engines respectively. The CNG-DI engine reduces 42% NOx emission as compared to the base engine. However, the CNG-DI engine produces higher HC and CO emissions as compared to the base engine. This paper discusses a review on the direct injection (DI) natural gas engine with new information along with other investigations. Ó 2011 Elsevier Ltd. All rights reserved. 1. Introduction High performance compressed natural gas direct injection (CNG-DI) engine development has now become a challenging and innovative technology. In particular, automotive engine researchers have sought this technology to improve engine efficiency with natural gas fuel to meet stringent emission limits. This innovative development will reduce emissions to limit the negative impact of the greenhouse effect. This investigation is related to in-cylinder direct injection based on Otto cycle and with an accelerating effort to design and develop better efficient engines while researchers have devoted significant resources to developing a CNG-DI engine. It is believed that the CNG-DI engine has great potential to optimise fuel supply and combustion, which in turn can deliver better performance and lower fuel consumption. Many researchers have conducted works on a CNG-DI system for diesel engines as in Refs. [1e6]. It is hoping that the output of this investigation and developing capabilities for advanced CNG-DI engine using gasoline cycle with spark ignition system will be a realisation of engineering dreams. 1.1. Reason for CNG-DI engine In conventional fuel injection systems natural gas is injected into engine cylinders either by a mixer, single-point injection or multi-point injection with electric motors. With all these injection systems, the natural gas engine produces lower brake power as compared to gasoline fuel. Hence, the CNG-DI engine system is more suitable where the fuel is injected through a high pressure pipe line straight into the cylinder with the required amount to produce similar or higher brake power than a gasoline engine. With the recent increase of oil price and limited reservation, it becomes necessary to accelerate the use of natural gas (NG) espe- cially for the automotive sector. Therefore, new technologies encompassing fuel systems, combustion chambers, control units, vehicle bodies, fuel storage and refuelling infrastructure also need to be investigated. The usage of NG in the transportation sector is increasing due to stringent emission regulations and limited fossil fuel reservation. Presently the manufacturer is involved in conversion of gasoline Abbreviations: CNG-DI, compressed natural gas direct injection; CNG-BI, compressed natural gas bi fuel; Gasoline-PI, gasoline engine with port fuel injec- tion; AFR, air fuel ratio; CAS, combustion analysis system; ECU, electronic control unit; MBT, maximum best torque; TWC, three way catalytic converter; MPI, mul- tiport injection; NG, natural gas; NOx, oxides of nitrogen; CO, carbon monoxide; HC, unburn hydrocarbon; WOT, wide open throttle. * Corresponding author. Tel.: þ60 379674459; fax: þ60 379675317. E-mail address: kalam@um.edu.my (M.A. Kalam). Contents lists available at ScienceDirect Energy journal homepage: www.elsevier.com/locate/energy 0360-5442/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.energy.2011.03.066 Energy 36 (2011) 3563e3571