Ethanol boosts MIT’s mini engine

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MIT researchers are developing a half-sized petrol engine that performs like a full-sized model but offers fuel efficiency approaching that of a hybrid engine at a far lower cost.

It uses a carefully controlled injection of ethanol directly into the engine's cylinders when climbing a hill or passing another road user.

The engine can go as much as 30 per cent farther on a litre of fuel than an ordinary engine, and provides high performance without the use of high-octane petrol.

The researchers believe that their ‘ethanol-boosted’ turbo engine has potential for widespread adoption and could have a significant impact on petrol consumption if widely adopted in the US.

The key to its development was using computer simulations to suppress knocking, which sometimes occurs from spontaneous combustion when efficiency changes are made to an engine.

When the engine is working hard and knock is likely, a small amount of ethanol is directly injected into the hot combustion chamber, where it quickly vaporises, cooling the fuel and air and making spontaneous combustion much less likely. According to the simulation, with ethanol injection the engine will not knock even when the pressure inside the cylinder is three times higher than that in a conventional SI engine. Engine tests by collaborators at Ford Motor Company produced results consistent with the model's predictions.

The engine is highly turbocharged so an engine of a given size can produce more power. It can also be designed with a higher compression ratio so the burning gases expand more in each cycle, getting more energy out of a given amount of fuel.

The combined changes could increase the power of a given-sized engine by more than a factor of two, so the researchers shrank their engine to half the size. Using computer models, they determined that their small, turbocharged, high-compression-ratio engine will provide the same peak power as the full-scale SI version but will be 20 to 30 percent more fuel efficient.

The engine should use less than five litres of ethanol for every 100 litres of petrol, so drivers would need to fill their ethanol tank only every one to three months.

Through their start-up company, Ethanol Boosting Systems, the researchers are working with their Ford collaborators on testing and developing this new concept. Vehicles with the new engine could be on the road within five years, using an alternative fuel to replace a bit of petrol and make more efficient use of the rest.