No abstract

Nowadays in many countries, where the conversion of internal combustion engines into alternative gas fuel is economically justified, the installation of CNG fuel systems dominates. According to official data, about 20 million vehicles with engines running on this fuel travel on the roads. Given the significant increase in the number of conversions carried out, special attention should be paid to the level of exhaust emissions of these vehicles. As many researchers show in their publications, combustion of this type of fuel emits less toxic compounds to the atmosphere than conventional fuels. Therefore, ecological aspects also speak for its use, which nowadays, mainly due to significant air pollution, are extremely important. In the case of conversion of vehicles with gasoline engines sequentially controlled by the engine controller, it is possible to adjust the adaptation of the parameters of this controller in various driving cycles, which affects the changes in vehicle emissions from the initial settings of this system. The article describes a number of bench tests that confirm the above statement. Extensive measuring equipment was used, which included, among others, the chassis dynamometer and exhaust gas analyzer. The results of the tests clearly showed that with the passage of using time of the vehicle (increasing mileage) one of the parameters in the control system changes significantly, which also changes the level of exhaust emissions. Unfortunately, this is an unwanted change. It has been suggested to counteract this phenomenon by emulating the lambda probe signal. The proposed solution has been implemented and tested. A series of exhaust emission tests of an engine equipped with a modified power supply system showed the correctness of the adopted solution.

Further restrictions on the use of compression-ignition engines in transportation are prompting the search for adaptations to run on other fuels. One of the most popular alternative fuels is Compressed Natural Gas (CNG), which due to its low carbon content can be competitive with classical fuels. This paper presents the results of testing a Cummins 6BT compression ignition engine that has undergone numerous modifications to convert to CNG power. The sequential gas injection system and the ignition system were installed in this engine. The compression ratio was also lowered from 16.5 to 11.5 by replacing the pistons. Tests conducted on an engine dynamometer were to show the differences in emission and conversion in the catalyst of hydrocarbons contained in the exhaust gases. Two structurally different catalysts operating at different exhaust temperatures (400 and 500)±2.5°C were used. The catalyst operating at 500±2.5°C showed a 23.5% higher conversion rate than the catalyst operating at a lower temperature in the range of the speed range tested. Also the external indicators, such as power and torque for the case of higher operating temperature took values over 70% higher. The research is one of the stages of a comprehensive assessment of the possibility of adaptation of compression ignition engines to CNG-only fueling.