Performance Improvement and Emission Reduction of NGV BiFuel Engines for Passenger Cars

Reduced resources of mineral oil and growing world energy consumption will increase the demand for alternative energies. Natural gas is gaining interest due to the worldwide ratio of assured reserves of natural gas and crude oil shifting towards natural gas. The main motivation for the use of gas are oil substitution, source diversification and independency of fuel supply as well as the reduction of greenhouse gases especially CO₂.

Natural gas operation usually reduces the torque of a naturally aspirated engine due to fuel properties. The paper shows that an optimization of a naturally aspirated engine layout can reduce the loss significantly. Besides compression ratio optimization also intake manifold and camshaft redesign for natural gas specific application can reduce the torque loss to a minimum.

Super charging or turbo charging of spark ignition engines can effectively overcome the torque loss. The development of a vehicle with 1.8L turbo charged engine described in the paper shows the high potential in power and torque with an increase of more than 25% in break mean effective pressure (BMEP).

The excellent combustion quality with reduced engine out toxic emissions and low smog formation potential as well as low particulate level currently allows relatively low emissions even without aftertreatment devices and leads to large conversion programs in areas with high local pollution. The current article describes how ultra low emission standards can be reached in combination with modern engine control technology strategies and advanced catalyst layout.