Trends in Performance Characteristics of Modern Automobile SI and Diesel Engines

A prior study (Chon and Heywood, [1]) examined how the design and performance of spark-ignition engines evolved in the United States during the 1980s and 1990s. This paper carries out a similar analysis of trends in basic engine design and performance characteristics over the past decade. Available databases on engine specifications in the U.S., Europe, and Japan were used as the sources of information. Parameters analyzed were maximum torque, power, and speed; number of cylinders and engine configuration, cylinder displacement, bore, stroke, compression ratio; valvetrain configuration, number of valves and their control; port or direct fuel injection; naturally-aspirated or turbocharged engine concepts; spark-ignition and diesel engines. Design features are correlated with these engine3s performance parameters, normalized by engine and cylinder displacement. Performance improvements (expressed as brake mean effective pressure, BMEP, and specific power) in fixed-valve-timing engines over the past decade have been modest; variable-valve control engines have improved more significantly, and substantially increased their market share. The number of naturally-aspirated engines with cylinder deactivation is growing. The percentage of turbocharged engines has increased steadily. Direct-injection gasoline engines have also increased market share, often combined with turbocharging. Compression ratios for diesels have decreased as high-speed direct-injection engines replaced indirect-injection engines, and their BMEP values have increased. For gasoline engines, compression ratio has been increasing steadily, and is about half a ratio higher in Europe (10.5) than in the U.S. (10.0) and slightly higher in Japan (10.2). Established scaling laws for normalized engine performance continue to give good correlations over the full range of engine sizes, for each different type of engine technology. The origins of such differences in performance are differences in engine breathing, compression ratio, use of direct fuel injection and steadily increasing maximum mean piston speed.