Development of BS-III Open Loop CNG Engine for a Mini-truck

Environmental degradation is on the rise due to an increased motor vehicle population. One of the strategies adopted to curb deteriorating environmental quality is the use of alternative fuels like Ethanol, Compressed Natural Gas (CNG) and Liquefied Petroleum Gas (LPG). Natural gas is the world’s most plentiful combustible fuel, abundantly available in all the continents. This naturally occurring fuel requires little or no treatment prior to use as compared to liquid petroleum products. Natural gas is also a low cost fuel.

This paper describes the open loop dedicated CNG engine development concept on a single cylinder engine. Water cooled Indirect Injection (IDI) diesel engine was converted to operate on natural gas with electronic ignition timing having a feature of change the spark ignition timing in regards to speed. In the CNG mode raw emissions and open loop Air/Fuel ratio for two Compression Ratios (CR) (9:1 and 11:1) were analyzed for hemispherical piston bowl geometry. Other exercises included study of exhaust emission of vehicle for CR (11:1) with/ without 3 way catalytic converters. Effect of different precious metal loading on exhaust emission was also studied.

The intake system length and air pre-filter area was optimized to maintain Air/Fuel ratio at stoichiometric values (0.98 to 1.05) with open loop gas supply system. Optimized compression ratio (11:1) shows 9-10% improvement in power and 8-11% improvement in brake specific fuel consumption. Engine was optimized with 3 way catalytic converter for proposed Bharat Stage-III (BS-III) norms with 48 % margin in CO, 70% margin in HC and 36 % margin in NOx.