Lotus Engineering says that in the initial phase of its ‘Omnivore’ flex-fuel engine development, the two-stroke engine has achieved a 10% improvement in fuel consumption compared to stratified direct injection engines.
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Lotus maintains that the research signals a potential paradigm shift with engine ‘upsizing’ for increased fuel economy.
The first testing phase of Lotus Engineering’s Omnivore variable compression ratio, flex-fuel direct injection two-stroke engine has been successfully completed on gasoline.
In addition to the ‘exceptional’ fuel consumption results, Lotus says the engine has successfully demonstrated homogenous charge compression ignition (HCCI) – where the engine operates without the need for the spark plug to ignite the fuel and air mixture in the cylinder – down to extremely light loads.
Traditionally, this has been challenging but this combustion process results in ultra low emissions and has been achieved over a wide range of engine operating conditions, even from cold start.
The detailed research has so far focused on lower speed and load conditions that represent a major proportion of an engine’s operation in a real world environment. At 2000rpm and up to approximately 2.7 bar IMEP (Indicated Mean Effective Pressure), the ISFC (Indicated Specific Fuel Consumption) achieved is approximately 10% better than current spray-guided direct injection, spark ignition engines. Emissions results are 20 ppm NOx at less than 2.3 bar load and has four-stroke-equivalent hydrocarbons and carbon monoxide emissions.
Simon Wood, Technical Director of Lotus Engineering said: “These impressive results represent an important step-forward in Lotus Engineering’s strategy of developing an array of more efficient multi-fuel combustion systems. Omnivore lays the foundations for a novel and pragmatic vision of a variable compression ratio engine concept suitable for production. A multi-cylinder version is practical for a wide variety of vehicles and offers greatest benefit to C and D class passenger cars which can take advantage of the low cost architecture and significantly improved fuel economy and emissions. We are continuing our discussions with other manufacturers and eagerly anticipate the development of multi-cylinder demonstrations of this revolutionary engine configuration.”
The Omnivore engine concept achieves wide-range HCCI combustion and low CO2 emissions through the application of a simple wide-range variable compression ratio mechanism, itself facilitated by the adoption of the two-stroke operating cycle. Technologies combined in this package are all synergistic, according to Lotus, and provide a route to the efficient use of alternative fuels, accelerating the displacement of fossil fuels.
Jamie Turner, Chief Engineer of Powertrain Research at Lotus Engineering said: “The automotive industry, including Lotus Engineering, has quite rightly advocated engine downsizing for four-stroke engines. This is as a result of the dominance of the four-stroke cycle in the automotive world and its generation of throttling losses at part-load, where vehicles run most of the time. The two-stroke cycle, conversely, does not suffer from significant throttling losses and in many ways is a more natural fit for automotive use.
“With the thermodynamic disadvantages of throttling losses removed, the two-stroke engine is free to be sized according to its improved part-load fuel consumption. Downsizing therefore isn’t vital and, due to the improved light-load efficiency and emissions performance we see with Omnivore, this technology approach and ‘upsizing’ could permit a more efficient engine.”
The initial Omnivore programme has been undertaken in 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.
Future work by Lotus Engineering will concentrate on further investigating the operation on gasoline and alternative renewable fuels such as ethanol and methanol, with more in-depth analysis of specific test points.
See also:
FEATURE: Rethinking the combustion cycle
UK: Lotus to unveil flex-fuel engine concept
