Search Results

Previous investigations have shown that fuel economy gains are possible in vehicles with increased compression ratio engines that meet 1978 Federal emission standards using oxidizing converter-EGR emission control systems. There has been no incentive to raise compression ratios, however, since the vehicle gains are offset by energy losses in the refinery due to refining the higher octane unleaded fuel required by high compression ratio engines. This paper discusses the application of an electronic closed loop knock control system to a higher compression ratio engine to allow operation on 91 Research Octane Number fuel. Two cars with different compression ratios are compared with both oxidizing converter - EGR and 3-way oxidizing-reducing converter-EGR closed loop carburetor emission control systems.

NOx emissions can be controlled through engine operation with lean homogeneous air/fuel mixtures. This emission control approach precludes the need for exhaust gas recirculation (EGR) and secondary air injection systems. The Lean Mixture concept results in similar emissions, fuel economy, and driveability when compared to EGR systems tailored to similar emission levels with similar aftertreatment systems. The Lean Mixture approach does offer the potential for less engine emission control hardware. The minimum NOx level achieved experimentally at the lean driveability limit was about 1.2 g/mi but with significantly higher HC emissions. Lean Mixture systems are sensitive to variations in engine air/fuel ratio which produce a significant effect on their emissions and fuel economy.

This paper describes the results of a study to evaluate the relationship of compression ratio on fuel energy conservation with the constraint of the 1977 Federal emission standards (1.5 HC, 15.0 CO and 2.0 NOx). The influence of the energy losses in the refinery process to produce higher octane fuels was considered as well as the effect of compression ratio on engine efficiency. Two different emission control systems were evaluated; a catalytic converter-EGR system and a manifold reactor-EGR system. These systems were evaluated on six vehicles; three intermediate size with 350 CID engines at compression ratios of 7.4, 8.3 and 9.2:1 and three sub-compact size with 151 CID engines at the same three compression ratios. Based upon total energy conservation, there does not appear to be an incentive for increasing unleaded or leaded fuel octane levels to allow for the use of higher compression ratios with converter-EGR or reactor-EGR control systems at the 1977 Federal emission standards.