Effect of Reduced Boost Air Temperature on Knock Limited Brake Mean Effective Pressure (BMEP)

The effect of low temperature intake air on the knock limited brake mean effective pressure (BMEP) in a spark ignited natural gas engine is described in this paper. This work was conducted to demonstrate the feasibility of using the vaporization of liquefied natural gas (LNG) to reduce the intake air temperature of engines operating on LNG fuel. The effect on steady-state emissions and transient response are also reported. Three different intake air temperatures were tested and evaluated as to their impact upon engine performance and gaseous emissions output. The results of these tests are as follows. The reduced intake air temperature allowed for a 30.7% (501 kPa) increase in the knock-limited BMEP (comparing the 10°C (50°F) intake air results with the 54.4°C (130°F) results). Exhaust emissions were recorded at constant BMEP for varying intake air temperatures. The raw BSNO_x emissions were reduced by 0.6% (0.1 g/kW-hr, not a significant change) due to the chilled air, but the corrected BSNO_x emissions were reduced by 17.8% (3.4 g/kW-hr). The BSHC emissions were reduced by 39.9% (0.5 g/kW-hr). The BSCO emissions, however, were increased by 7.5% (0.2 g/kW-hr). Transient engine response revealed that the use of reduced temperature intake air provided a 15.3% (1.43 second) improvement in the time required to obtain an engine speed of 1600 rpm. Similarly, the chilled intake air reduced the time required to reach a set manifold air pressure of 212.4 kPa (30.8 psia) by 11.5% (1.21 seconds).