- Intake: Starting near the top of the cylinder, the piston travels downward, drawing in a mixture of air and fuel.
- Compression: The piston reaches the bottom of the cycle and starts moving upwards, compressing the air/fuel mixture.
- Power: As the piston nears the top of the cylinder, the spark plug ignites the air/fuel mixture. This causes an increase in pressure that presses the piston downward again.
- Exhaust: By the time the piston reaches the bottom of it's stroke, all the fuel has combusted. When the piston reverses direction it forces the exhaust products out of the engine and the cycle starts again.
This means that each cylinder is pulling double duty. A cylinder will use one reciprocation to intake and compress the air and fuel, and the next reciprocation to ignite and exhaust. A split-cycle engine shares this load between two cylinders: one for intake and compression, one for power and exhaust.
I first heard of Scuderi's split-cycle engine way back in 2006. At that time, they just had some ideas and computer models. Now they've released some more information, including extended testing with a prototype engine. Based on this prototype, they project fuel efficiency improvements of up to 36 percent over standard gasoline engines.
There's a significant improvement in power density as well. The prototype is a 1 liter, 2 cylinder engine producing 135 horsepower at 6,000 RPM. To put that in perspective, my car has a 2 liter, 4 cylinder engine and, despite the doubling in cylinders and volume, only generates 5 more horsepower.
I won't delve too deep here, but Scuderi also have plans to build a regenerative braking system into their engines. The power/exhaust piston is shut off while the vehicle brakes, and this basically makes the engine into a fancy air compressor. The compressed air is stored in a tank, and when the car takes off again the intake/compression piston is shut off while the engine runs off its reserve of compressed air.
I know, I know. Internal combustion is so last century! But there's too much technological inertia, and too much oil in the ground, to make a clean break. Current hybrid automobiles try to bridge this divide, but their power-trains are heavy and complex. They have to carry a complete internal combustion engine, plus batteries and an electric motor. The Scuderi design is a better compromise because it is simpler, lighter, and ultimately cheaper.