65 MPG Split-Cycle The Next Direction For Gasoline Engines?

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Scuderi twin-cycle Miller gasoline engine

Scuderi twin-cycle Miller gasoline engine

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Like it or not, the humble gasoline engine still has a lot to give to the automobile world.

Yes, they use fossil fuels that could be better used elsewhere, but while pure electric vehicles and even hybrids remain relatively expensive, improving the efficiency of regular internal combustion engines is a good way of reducing pollution and dependency on gasoline.

There are still more avenues to be explored, too. One such route is the split-cycle engine, which American engineering firm Scuderi has just filed for patent after several years development.

You might want to grab a coffee at this point, as we're about to get technical...

Most internal combustion engines run on the four-stroke induction, compression, ignition and exhaust "Otto" cycle.

It's otherwise known colloquially as "suck, squeeze, bang, blow", because that's essentially what happens - air is drawn into the combustion chamber where it mixes with injected gasoline (suck), the piston rises to compress the mixture (squeeze), the spark plug fires, igniting the mixture and pushing the piston down to provide power (bang), and as the piston rises again the exhaust valve opens, and the exhaust gases are pushed out of the cylinder (blow).

Atkinson cycle engines, as used in several modern hybrids (including Fords, Toyotas and Mercedes-Benz), operate similarly, but leave the intake valve open a little longer, while the piston is in the "squeeze" phase.

Compression is reduced, but expansion remains the same. Atkinson cycles extract more energy from combustion, but produce less power. This is good for emissions, and the power deficit can be compensated for by the extra shove of the electric motor.

Miller cycle engines are very similar, but use forced induction - usually a supercharger - to make up the lost power by forcing more air into the combustion chamber.

Scuderi's split-cycle engine is a Miller-cycle engine, but splits the suck, squeeze, bang and blow between two cylinders - one doing half the work, the other doing the other half. Compressed combustible mixture is pushed from one cylinder to the other, through a special port.

This sounds complicated, but each of the four strokes is completed in only one crankshaft revolution, rather than the two of a regular engine.

Just tell me what this all means!

Essentially, the engine can do more work per crankshaft revolution. The paired cylinders work as a team, rather than every man for himself. While one is drawing in air and fuel, the other is already combusting the last cycle's mixture.

Because it's doing more work, you need no more cylinders than normal - two pairs, or four cylinders in total, for example - but the engine uses less fuel as fewer cylinders are burning fuel and air.

Using a Miller cycle approach, it burns cleaner, and a turbocharger makes up for the lost induction volume.

Even simpler, please...

The net result, Scuderi says, is an efficiency gain of 25 percent over European "high economy" vehicles on average, and 13 percent more efficient than even the current best in class vehicles.

In cold, hard numbers, Scuderi predicts figures of up to 65 miles per gallon from a Scuderi-powered vehicle. CO2 emissions would be reduced too, with a predicted figure of 81.6 grams per kilometer, compared to Europe's fleet-wide target of 120 g/km.

Naturally, as the split-cycle engine is still just a combustion engine, it could see wider use, potentially making hybrid vehicles more efficient, for example.

If you'd like to know more on Scuderi's engine, there are several links on the company's website.

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