Lotus Tests the Two-Stroke “Omnivore” Engine
Source: CNET Green Tech
Last year, Lotus announced the development of its Omnivore engine, the name denoting flex fuel capability. Today Lotus released test results for the engine, along with the kind of detail on how it operates only an engineer could love. These test results cover the first phase of testing the Omnivore engine with gasoline. Presumably, testing with fuels derived from alcohol and other sources are in the next phases.
In Lotus’ lab, the Omnivore engine brought in 10 percent better fuel economy than current direct injection engines, which are the most efficient on the market.
Two-stroke engines have twice as many “power strokes” at any given RPM when compared to the common four-stroke engines, making them more powerful and naturally efficient. (The engine is not “wasting” as much energy moving the piston up and down in power-robbing intake and scavenging strokes.) Two-strokes are smaller and lighter when compared to four-stroke engine of similar horsepower, and have fewer moving parts that simplifies the inner workings, making them cheaper to build and maintain.
In the past, the problem has always been pollution – it was considered near-impossible to build a two-stroke engine that could meet modern emission standards. Apparently Lotus is solving this problem:
Omnivore also uses a two-stroke, rather than a four stroke cycle, but still manages to turn in emission levels equivalent to modern production engines.
This Lotus prototype engine uses an ignition system called “homogeneous charge compression ignition (HCCI), meaning that instead of igniting its fuel charge with a spark plug, the compression of the cylinder causes the charge to ignite, similar to a diesel engine.”
More good news – the prototype is a flex-fuel engine, which would allow the owner/operator to choose what kind of fuel preferred to power it with – fossil-fuel gasoline (and diesel?) or bio-mass alcohol (ethanol/methanol) or a combination of the two.
Flex-fuel engines already exist, the problem with the current crop is that they are engineered as gasoline engines, and re-programmed to also run on alcohol blends – meaning that mechanically they are still designed for the lower compression ratios required to run on modern gasoline blends. Alcohol fuels have “less energy” per gallon than gasoline, but can run at a much higher compression ratios, allowing a properly-built alcohol engine to “gain” additional efficiency and reduce the “MPG” gap with gasoline.
The Lotus engine can apparently modify it’s compression ratio thanks to what they call the “puck” – or the “variable compression mechanism…at the top of the cylinder which dynamically changes the displacement depending on running conditions.”
Once again innovative engineering is proving that there still are many ways to improve fuel efficiency with the internal combustion engines, and there are no technical reasons we can’t be driving cars that get 60+ MPG regularly. The “fuel efficiency flat-line” from the mid-1980’s until just recently was due to something else – not because it was “technically impossible” to build more efficient engines.