1. Abdullah, M. A. (2009). Engine Performance and Combustion Characteristics of Hydrogen in a Direct Injection Engine. M. S. Thesis. UniversitiTeknologi PETRONAS. Perak, Malaysia.
2. Ahmad, N. and Babu, M. G. (2006). Simulation and experimental studies on combustion and performance characteristics for a turbocharged and naturally aspirated multi-cylinder compression ignition engine. SAE Paper No. 2006-01-3487.
3. Aziz, A. R. A. and Firmansyah (2009). The effect of fuel rail pressure on the performance of a CNG-direct injection engine. SAE Paper No. 2009-01-1498.
4. Balawant, S. T. (2012). Experimental investigation on effect of combustion chamber geometry and port fuel injection system for CNG engine. IOSR J. Engineering (IOSRJEN) 2, 7, 49–54.
5. Cho, H. M. and He, B.-Q. (2007). Spark ignition natural gas engines - A review. Energy Conversion and Management 48, 2, 608–618.