Two-stroke makeover offers a glimpse into a fuel-efficient future for car engines.
Two-stroke engines are dirty and noisy; that’s the common perception at least. But according to engineers at Lotus, a new breed of ultra-efficient two-stroke, a world removed from the puttering, dribbling power-train of the low-cost moped, may one day steal the four-stroke’s thunder.
The initial programme was carried out in collaboration with Queen’s University Belfast and Orbital Corporation Australia. Lotus is now looking for further backing to share the risk and to take the project to the next level, which would involve developing a multi-cylinder variant and ultimately fitting a test engine to a car. So far, said Turner, the concept has certainly generated plenty of excitement. ’We’ve had a lot of interest from OEMs, which is good because everyone’s grappling with how to get CO2 down in the future so we’re hoping to form some kind of consortium that will enable us to fully map the engine and take the engine design forward. I believe the engine has significant legs on it.’
There’s a long way to go before the engine makes it anywhere near a car — Turner estimates three years with a favourable wind — but considering how fundamentally different it is, the project has already come a long way.
Recalling the light-bulb moment when a colleague suggested putting a VCR system in a two-stroke engine, Turner believes the new engine is a great example of the importance of a creative, cerebral approach to engineering. He finished by saying: ’The overall process was one of invention rather than computation. You would not have arrived at this solution through just running endless computer simulations, because pretty much all of the tools that the industry uses are based around four-stroke engines.’
Two-stroke cars
A number of manufacturers have used two-stroke engines in the past
- 1950 Swedish car-firm Saab introduces a two-stroke engine on the Saab 92, based on the design of the German car marque DKW
- 1955 Suzuki launches the Suzuki Suzulight (360cc, two stroke) which helps to usher in Japan’s light-weight car age
- 1957 East German car maker VEB Sachsenring launches the infamous Trabant 500, the first of three versions of the Soviet-era car to be powered by a two-stroke engine
- 1964 DKW launches the F102, the last in a long line of two-stroke engined cars and the direct forerunner of the first post-war Audi (which used a conventional four-stroke engine)
What about the lubrication problem? In a 4 sroke the oil is kept in the crankcase by the piston rings. In a 2 stroke the oil is carried around with the charge and gets burned in the combustion chamber;this is true even when the oil is directly injected into the big ends and the cylinder walls – some of it inevitably combines with the charge and is burned producing the familiar blue haze from the exhaust pipe. Why not revive interest in sliding-sleeve 4 strokes where the culinder walls are ported and are controlled by the rotating cylinder sleeve, these always burned a bit of oil but the oil loss was more controllable than in the case of a 2 stroke.
neat, but no throttle then ??
And the crankcase is a wet-sump ?
It’s very neat. Some of this technology is of very large marine engines. Wet sump is possible because the induction is over the top of the piston through a cylinder wall port opposite the exhaust port (with the trapping valve). Robert Taylor misses this point with his post recalling that the “old style” 2 strokes prepare the induction air in the crankcase and “transfer ” it to the combustion space on BDC. Like large marine engines this could benefit from supercharging to assist scavanging, but then the video is very over simplified. The text clearly states that there is no spark plug, but there is definitely something in the VCR system which is assisting initiating the combustion, a glow plug type device perhaps? One last thing varying the engine speed with an injection system does not necessarily require a “throttle”, fuel mixture can be controlled by varyng the fuel quantity (again like diesel direct injection engines) As the story explains; there is a lot to be gained in emmissions by keeping the air volume (mass) at a maximum and burning as much fuel as is required to produce the desired power. The variable compression ratio allows the control of the “knock” and point of ignition. I can well understand the excitment at Lotus on this one.
Yep! – I couldn’t access the video initially – I should have waited!
How dose this compare to a 2 stroke, direct injection diesle ? Variations/design
information have been around for year’s.
One could go back and dig up alot of usefull engine designs as a basis, and couple them with new digital designs(ing).Year’s ago, while as an assistant, serveying across a farmers field.We came acoss an abandoned open seated
grader, still olive drab. The owner/farmer
was in the vicinity ( he was alway’s keeping a close watch, as he misstrusted
us ) So, seeing a chance to break the ice.I asked him about the, green grader, and he lit up, saying what a great piece of engineering it had been. He said it was
started with gasoline, it had a carburetor,
and spark plugs. But once warmed up,with the turn of some valves, it would
cough to life as a diesle,” or just about anything you could pour and put a match to” The farmer said he abandonded it when he could no longer find any military surplus parts.
So, now we think we’ve got it made with
engine designing ? Maybe it’s time to take a look back in time, Mike