Turbocharging captures escaping exhaust, or wasted energy, and forces it to spin a turbine that forces clean air into the engine's intake manifold rather than using the engine's own energy to suck it in. This rush of air creates extra torque and horsepower, enabling a small, more fuel-efficient engine to generate the acceleration power of a large, more fuel-thirsty engine. There is as much as a 30 percent to 40 percent net gain in power with turbocharging -- not only from the efficiency of the air delivery system, but also through the weight savings of a smaller, lighter engine.
Direct fuel injection. Most fuel-injected engines use indirect fuel injection that premixes the air and fuel in the intake manifold. With direct fuel injection, the air still arrives in the cylinder through the intake manifold, but the fuel is injected directly into the cylinder separately.
Because direct fuel injection uses extremely advanced computer management, it is very precise regarding the amount of fuel injected but also exactly when it is injected. Additionally, direct fuel injection produces a finer mist of fuel than indirect injection, which burns more completely thus reducing waste.
Direct fuel injection is a more expensive system to build than indirect fuel injection, and consequently, its use has not been widespread. Its attraction, however, is that it increases power significantly -- 40 percent in the Cadillac CTS -- over indirect fuel injection with virtually no loss of fuel economy.
Homogeneous Charge Compression Ignition, or HCCI. Ever wondered why diesel engines get better fuel economy than ICEs? One reason is HCCI. Gasoline engines use a sparkplug to ignite the fuel-air mixture in the cylinder. Diesel engines instead use the heat created by the compression itself to ignite the fuel-air mixture.
GM is currently developing an HCCI system that includes other enabling technologies, such as direct fuel injection and combustion pressure sensors. In the Saturn Aura HCCI concept vehicle, the HCCI uses a traditional spark ignition system. HCCI carries the load at idle and at speeds up to 55 miles per hour, when the traditional spark ignition system kicks in.
GM claims fuel savings of up to 15 percent with HCCI, which is expected to provide fuel economy approaching that of a diesel, but without high levels of nitrogen oxides found in diesel exhaust and the expense of after-treatment systems required to scrub out the nitrogen oxides.
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