In recent years, engine innovation has been driven by the quest for better fuel economy with equal performance. Government regulation and rising fuel prices are forcing automakers to develop new, more efficient technologies. In years to come, we will see more vehicle/engine downsizing, and hybrid and “clean diesel” vehicles. The average fuel economy in 2011 was 27.3 mpg about what it has been for the past decade. The average for cars was 30.2 mpg, and 24.1 mpg for light trucks. SUV and trucks represent more than half of the auto sales in the US, and are dragging down the average fuel economy overall. By the 2016, the government wants passenger cars to achieve an average of 39 mpg, and trucks 30 mpg with a combined average of 35.5 mpg. This will save an estimated 1.8 billion barrels of oil, and 900 million metric tons of greenhouse gas emissions. How will the car makers reach these targets? By downsizing vehicles, reducing vehicle size and weight and using smaller, more fuel-efficient engines.
Hybrids have been popular recently, yet only make up 2.5% of all new vehicle sales. Hybrid production is limited by the cost to produce (about $3000 extra per vehicle on average) and limited battery production. By 2016, the number of hybrid/plug-in electrics is expected to grow to 1.5 million. By comparison, “clean diesel” sales are expected to skyrocket from 680 thousand to more than 9 million by 2016. In Europe, more than half of all new car sales are diesel engines.
Rising Fuel Economy
Gasoline-powered internal combustion engines have evolved since the early days of the automobile. Emissions controls required in the 1960s and 70s hindered performance, but made engines more efficient than ever before. The biggest increases by far came from the invention of electronic fuel injection and engine management, and the reduction of friction between internal mechanisms.
Turbocharging and supercharging also boosted fuel economy by allowing smaller four- and six-cylinder engines to create as much power as a V8. A turbocharger works by using the hot exhaust gases to spin a turbine to compress more air into the cylinders. A supercharger uses a belt driven compressor to add boost pressure. Super chargers are used primarily on performance cars while turbochargers are used on a broad spectrum of vehicles. Gasoline Direct Injection (GDI) also helps improve fuel economy by injecting gasoline directly into the combustion chamber rather than the intake port. It is estimated that one of every five vehicles produced next year will have GDI fuel systems.
Waste Not, Want Not
Cylinder deactivation increases low load fuel economy on certain engines by 10-20%. Cylinder deactivation should not be confused with Variable Valve Timing (VVT). VVT uses cam phasers on the ends of the camshaft(s) to either advance or retard the relative timing of the cams. Oil pressure moves a mechanism inside the cam phaser that allows the gear to slide a few degrees one way or the other to alter valve timing.
Down The Road
In the not too distant future, a number of new technologies will be used to improve fuel economy. One such technology would be the elimination of the starter motor using direct injection to start the engine. With direct injection, gasoline engines will increase their compression rates to almost match those of diesel engines. Smaller displacement engines with turbos will replace naturally aspirated V8s and V6s. Future turbos may be driven by an electric motor rather than hot exhaust gases. An electric-powered turbo can spool up independent of engine speed or load to deliver instant boost, and getting rid of the exhaust-driven turbine wheel also gets rid of the heat, allowing the turbo to run much cooler and last much longer. Variable valve timing may also be used to create unconventional compression and power strokes. These include an “Atkinson” compression cycle where the valves are opened later to create a longer power stroke, or a “Miller” cycle where the intake valves are opened longer than normal during the compression stroke. Both techniques improve breathing efficiency and power but require other tricks to make them work. High speed electric solenoids such as those used in some Formula 1 engines may eventually find their way into some production engines, eliminating conventional cams, lifters and rockers altogether.
Nobody sees impending doom for piston engines (gasoline or diesel) anytime soon. Though there are some electric cars that use no gasoline or only for extended range driving, those vehicles will be fairly limited due to costs.