Talk fuel efficiency and words like "direct injection," "flex-fuel" and "variable compression ratio" are common. But they aren't usually combined with "two-stroke." Unless you're Lotus that is.
We first showed you the Lotus Omnivore engine back in August, speculating that, when completed, it could change the future of internal combustion engines. Well here it is.
The Omnivore is a single-cylinder engine using a variable compression ratio, two-stroke cycle and direct fuel injection. The three systems combined mean that it can operate more efficiently than four-stroke engines using a variety of fuels ranging from anything alcohol-based to normal pump gasoline.
The variable compression ratio system takes advantage of the two-stroke's lack of poppet valves to build a moveable puck into the top of the cylinder head. It works very simply, sliding up and down inside the cylinder to alter the compression ratio. This helps it run on a variety of fuels regardless of octane.
Direct injection also helps optimize the Omnivore for a variety of fuels. The system is capable of directing the right amount of fuel into the cylinder at the correct moment for its type. This helps avoid the issue of pre combustion under high pressure by tailoring the injection to the fuel type.
The two-stroke cycle is something largely thought killed by emissions regulations. They run a total loss lubrication system, meaning the lubricant is burned with the fuel. Clouds of blue smoke are not environmentally friendly. But here, able to run higher pressures, the engine should more completely burn anything that ends up inside it, leading to reduced emissions. Of course there's also increased power available over an equivalent four-stroke thanks to twice as many power strokes. This allows the engine to be smaller and lighter.
All three of these technologies are combined with a monoblock construction that combines the cylinder head and block together, eliminating the need for a head gasket, improving durability. It all appears to be an extremely elegant solution which could preview the future of considerably more efficient, lighter, simpler engines capable of running an both bio-fuels and old timey gasoline. Diesel fuel is also conceivable, although its not specifically mentioned by Lotus. Here's hoping this engine finds its way into a concept car in the near future, quickly followed by production. It could be just the thing to power a hyper fuel-efficient Lotus Elise.
The press release follows:
Lotus Omnivore Research Engine Unveiled
Lotus reveals flex-fuel engine concept to maximise fuel efficiency when running on renewable fuels or gasoline
Lotus Engineering, the world-renowned automotive consultancy division of Lotus Cars Limited, unveils its latest research into engine efficiency at the 79th International Geneva Motor Show. The Omnivore engine concept has the potential to significantly increase fuel efficiency for sustainable alcohol based fuels, which increases the prospect of a greater amount of vehicle miles travelled using renewable fuels. On display will be the single cylinder research engine monoblock that demonstrates the novel architecture designed for high thermal efficiency when fuelled on any alcohol based fuel or gasoline.
The Omnivore concept features an innovative variable compression ratio system and uses a two-stroke operating cycle with direct fuel injection. It is ideally suited to flex-fuel operation with a higher degree of optimisation than is possible with existing four stroke engines.
The engine concept features a monoblock construction that blends the cylinder head and block together eliminating the need for a cylinder head gasket, improving durability and reducing weight. In this case, the application of a monoblock is facilitated by the absence of the requirement for poppet valves. A novel charge trapping valve in the exhaust port allows asymmetric timing of exhaust flow and continuous variation of the exhaust opening point.
The variable compression ratio is achieved by the use of a puck at the top of the combustion chamber. This simple, yet effective system moves up and down affecting the change in geometric compression depending on the load demands on the engine.
Mike Kimberley, Chief Executive Officer of Group Lotus plc said: "We are delighted to unveil this major milestone in the development of an engine configuration for a new breed of more efficient multi-fuel engines. The automotive sector is focusing on its environmental obligations to improve efficiency, minimise reliance on fossil fuels and reduce harmful emissions and Lotus continues to be an industry leader through our work on all aspects of future fuels. Sustainable alcohol based fuels have the potential to reduce the overall CO2 footprint of internal combustion engines towards zero and for this reason, need to be embraced as future fuels for road transport."
In this collaboration with Queen's University Belfast and Orbital Corporation Limited Australia, with sponsorship from DEFRA/DECC and DOE NI through the Renewables Materials LINK programme, Lotus Engineering is currently in the final stages of commissioning the Omnivore single-cylinder research engine. It uses the Orbital FlexDI™ fuel injection system which produces fine in-cylinder fuel preparation irrespective of fuel type, and together with air pre-mixing allows efficient two-stroke combustion and low-temperature starting, whilst offering singular opportunity for advanced HCCI control.
The Omnivore programme is another development of Lotus' research into understanding the complex combustion processes involved in running an engine on mixtures of alcohol based fuels and gasoline, which included the Lotus Exige 270E Tri-fuel, unveiled at the International Geneva Motor Show in 2008. This research is vitally important for a successful transition from today's fuels to the more efficient sustainable fuels of the future.
Geraint Castleton-White, Head of Powertrain at Lotus Engineering said, "The absence of poppet valves in two-stroke engines makes the incorporation of a variable compression ratio system relatively straightforward. Our research into these systems on four-stroke engines has led us to the conclusion that while thermodynamically it is a desirable technology to incorporate, practically it is very difficult, particularly taking into consideration production feasibility. This two-stroke engine could solve these practical difficulties and simultaneously permits a much larger range of compression ratio adjustment, with the potential to perform at a much higher efficiency when running on renewable fuels."