But in order to push fuel efficiency figures higher, some designers are asking if we need a radical re-design of engines altogether.
“For over 100 years the conventional internal combustion engine has only been 33% efficient” says Bill Wrinn of engineering firm Scuderi, which has designed a new kind of engine. “It should be higher – if you put a gallon of gasoline in your tank, two thirds of it is wasted.”
Scuderi is developing an engine that still has pistons rising and falling in cylinders, but with one major difference. “What we do is we separate the four strokes,” says Wrinn. In one cylinder, we have 2 strokes that deal with compression, and then in the other cylinder we have 2 strokes that deal with exhaust.”
What that practically means is that air is drawn into the compression cylinder as the piston moves down, and then compressed as it moves back up. Rather than squirting fuel into this chamber, the compressed air is passed through a tube to a separate cylinder where fuel is injected and ignited to provide the power. A four cylinder engine working on this design would have two compression cylinders and two combustion cylinders.
“Because we can separate those two functions, we are able to maximize the compression process, and also maximize the combustion process, to make it a more efficient, cleaner combustion process” says Wrinn. In certain applications, Scuderi believes that this seemingly simple tweak can improve fuel efficiency by 40% or more.
At first glance, it looks like the Scuderi engine would have to have twice as many cylinders to make the same output, but that is not the case. It has a “power” stroke for every revolution of the engine, rather than every two.
The innovative design allows for some other clever ideas. Compression and combustion do not have to happen in sequence, and Scuderi are working on what it calls an “air-hybrid” system. Instead of electric generators storing energy in batteries, as happens in today’s hybrids, the engine can disable the combustion cylinder when a vehicle is coasting, and re-route the air from the compression cylinder into a storage tank. The highly compressed air can be released later to power the engine without any fuel.
Other radical engine redesigns have been proposed over the last century, but the automotive industry has been slow to move, partly because it has never had to. The internal combustion engine as we know it has been tweaked and improved, and has proven to be highly reliable, very safe and ultimately cheap to make.
“There are a lot of great engine ideas and concepts out there, but the reality is that with the industry as it is, and the economy that we have, it is a lot easier to go in smaller incremental steps. That is more conducive to the current assembly and production lines,” says Wrinn.
But Scuderi believes that its engine might be the one to finally knock the conventional four stroke off its pedestal. As well as improved efficiency, its basic architecture of cylinders and pistons is also very similar to a conventional engine.
“We are looking at around 95% or 96% of the same parts. We don’t have a lot of exotic materials,” says Wrinn.
The firm is now talking with manufacturers all over the world, but the engine is likely to make a first appearance in Asia. The company believes that car makers in countries like China are more willing to experiment. Once it is licensed, it will be around three to five years before we see a Scuderi powered vehicle on the roads, which will be just in time to help meet those new US efficiency standards.