The utilization of natural gas as fuel for future propulsion systems becomes increasingly important for urban air quality control. The main interest results from its potential to contribute to local and global air pollution reduction. The last decades have shown that, for a potential market introduction, alternative fuel technology not only has to offer significant environmental benefits, but also needs to compete with the conventional technologies, such as gasoline and diesel engines, on a basis of investment and operation cost. Tax incentives or other promotional efforts may be appropriate to support the initial introduction, but only competitive operational cost can persuade customers to hook on new technologies.
Within this paper, a new CNG combustion system approach for highly efficient, low polluting engine operation will be introduced. The concept configuration of the direct induction natural gas (DING) engine is being presented. Because of time-based fuel metering a very flexible setting of gas induction timing and quantity is possible. In general, the DING system represents a common rail type fuel metering system approach and is compatible with advanced technologies for diesel engines, including exhaust gas aftertreatment systems for nitrogen emissions reduction.
Since the combustion concept relies on unthrottled, inhomogeneous air/fuel mixture formation, high power density as well as a beneficial thermal efficiency, known from state-of-the-art diesel engine technology, can be maintained. An outlook is given on the performance, fuel economy and emissions benefits for engines operated with this technology and compared to state-of-the-art diesel and CNG engines. Finally, NGV conversion and operation cost aspects will be addressed based on a comparison of different bus and truck technologies required to meet future emissions standards.