ICE EFFICIENCY GAINS geometry turbochargers offer greater efficiency over a wide range of engine operation because the flow area can be controlled according to the available amount of exhaust flow and energy available from the engine. Electrically assisted turbochargers will become more common, so that the response of the engine boost is as fast as the driver can demand. This should reduce the mechanical and control complexity of some modern turbochargers and make the sizing of the turbo less of a compromise. ENGINE CONTROL We know that spark timing and injection timing have a significant impact on the performance and efficiency of engines. When both quantities were fixed or at least out of our fine control, engine performance was poor and throttle response unpredictable. With fuel injection and widespread use of turbocharging has come the motivation (through necessity) to exert better control over the events that control fueling and ignition, altering them in response to engine speed, temperature, humidity, air pressure throttle position and other factors. Compression ratio is another old favorite to which we continually return. Modern engine control gives precise fueling and spark timing, and we understand combustion better than ever before. FRICTION REDUCTION For someone with a background in racing engines, friction reduction is an ever-fruiting tree from which to pick. The low efficiency of the IC engine is due in large part to friction. Despite our best efforts to separate sliding pieces of metal from contact against stationary surfaces by interposing oil into the narrow spaces between them, friction remains a very significant contributor to inefficiency. Improved materials are better able to withstand repeated cycles of high stress, and improved lubricants can cope with high stresses, high shear rates and increased operating temperatures. Hydrodynamic RIGHT: Both active and passive turbulent jet ignition systems have found their way into production automobiles losses in bearings and sliding contacts are lower, and where it is not possible to keep surfaces in relative motion separated enough to ride on an oil film (very difficult in several places in an engine), the application of hard, durable and low-friction coatings has proved to be very effective at reducing friction and improving the durability of the sliding components. Weight reduction also leads to friction reduction and improved transient response; improved response leads to less time spent on the throttle. There are a few components that are especially potent in this respect, and where the engine designer is rewarded with gains throughout the engine. For instance, a lighter piston imposes a lower load on the piston pin, which can therefore be reduced in section. The lighter piston and pin produces lower inertia stresses on the connecting rod, so the rod can be reduced in mass. The lower reciprocating mass might allow narrower bearings or a smaller crankpin. It very definitely reduces the amount of counterweighting required to keep bearing loads within safe limits. Similarly, a light valve can be closed by a lighter spring, which can lead to a shorter valve and therefore a potential reduction in the distance from crankshaft to camshafts (for overhead camshaft engines). A small reduction in valve mass can therefore produce mass reduction in other parts of the mechanism, and a lighter cylinder head. This example of the benefits of mass reduction in the valvetrain is dealt with in the excellent paper by Kanzaki et al. 4 TJI There has been a great deal of research into combustion improvement. An idea adapted from large gas-burning engines (gas as in gas, not gasoline) and improved through development in Formula 1 and Le Mans racing shows great promise in terms of improving efficiency. Pre-chamber ignition, 38 www.automotivepowertraintechnologyinternational.com / March 2025
Automotive Powertrain Technology International Automotive Powertrain Technology International March 2025 Issue: Page 38
