Abstract

This paper presents the experimental results on brake power enhancement of a modified natural gas engine. Conventional natural gas engine produces 15 to 20% less brake power than that of gasoline fired engine. This lacking in compressed natural gas (CNG) engine needs to be recovered through modifications and optimization of fuel injection system to provide complete gas combustion in the engine cylinder. A multi-cylinder gasoline engine was modified to bi-fuel engine for operating in several test conditions, such as constant full and half throttle condition. Variation in power production with corresponding fuel flow rate and emission gases (such as carbon monoxides, CO; unburnt hydrocarbon, HC and nitrogen oxides, NO_x) were studied by using two fuels (gasoline and CNG). Engine tune up information like variation in air fuel ratio (AFR) for lean burn operation can be known from those tests. Performance of engine was studied with both the fuels at fixed load and the corresponding fuel flow rate and emissions were measured for evaluation and optimization. The engine produced 10% higher brake power with CNG fuel as compared to that produced with gasoline fuel at full load, but at partial load gasoline fuel produced more brake power than CNG. Emission results revealed that CNG fuelled engine emits less CO and HC, showing more complete combustion than gasoline fuel. On the contrary, higher combustion temperature of CNG fuel produced more NO_x than gasoline. The results of these investigations can be used to develop a new compressed natural gas (CNG), direct injection (DI) and higher efficiency engine in the near future to build an environment friendly fuel economic clean burning automotive vehicle with less emission and similar power rating like gasoline engine.

Key words: Brake power, compressed natural gas-direct injection (CNG-DI), bi-fuel engine, fuel consumption, emission.