Pilot ignited direct injection natural gas engines undertake significant advantages over conventional diesel engine with specific combustion mode. In this paper, extensive experiments have been carried out to provide further understanding of performance and heat release rate under different operating conditions. Through the experimental investigations and detailed analysis, it is demonstrated that shortened injection interval and diesel injection pulse width as well as increased injection pressure lead to an increase in maximum in-cylinder pressure and deteriorated combustion noise. The maximum heat release rate is raised by retarding injection timing, reducing injection interval, shortening diesel injection pulse width and increasing injection pressure. The stability of combustion shows uncertain trends with the variation of injection timing and pilot diesel injection quantity, while can be generally improved by the adoption of shorter injection interval and lower injection pressure. It is also revealed that fuel economy can benefit from the application of advanced injection timing, smaller diesel injection pulse width, shorter injection interval and higher injection pressure. (C) 2015 Elsevier Ltd. All rights reserved.