A New Pulsed Multipoint Injection System to Reduce Natural Gas Vehicle Emissions.

Nowadays, most of the natural gas conversion systems available on the market for bifuel vehicles are based on the venturi principle or on the continuous injection principle for the carburation of the engine. Even if the driveability of these systems is satisfactory, their emission performance does often not reflect the full environmental potential offered by natural gas. This is mainly due to the low response of these systems to transient conditions. During the past years, EPFL has been involved in a co-operative program with the industry to develop a new natural gas injection system intended for multipoint sequenced and phased indirect gaseous fuel injection. Mounted on a four cylinder 1.4-liter engine, the system includes specifically developed injectors and a PC based electronic control unit. Emission results on the engine test vench are shown for typical transient sequences as well as steady state conditions. Results on the chassis dynamometer are given for the New European Driving Cycle (94/12/EC directive). Keeping the standard vehicle components (like catalytic converter and lambda sensor), the current emissions results from our novel injection system are well below the legal emissions limits. Those results are compared with the performance of a state of the art multipoint continuous injection system from the market, measured on the same engine. In order to control accurately the narrower lambda window when working with natural gas, the system, among others, accounts for the sensitivity of the lambda sensor to the composition of the exhaust gases. While maintaining a good driveability, this system has shown significant emissions improvements compared to actual natural gas systems. New engine control strategies currently under evaluations are likely to still further reduce emissions.