Better two-stroke engines


in Geek stuff, Science, The environment

Apparently, it might be possible to make efficient two-stroke engines that are less polluting than their predecessors.

Improving the efficiency of gasoline and diesel engines is an important undertaking, both because it will be a while before electric vehicles are ready for near-universal urban deployment and because there will be rural vehicles running on fossil fuels for quite a while yet.

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{ 8 comments… read them below or add one }

Matt July 28, 2010 at 7:11 pm

Interesting topic.

As mentioned in the article, 2 stroke gasoline engines have generally been considered smoky and inefficient due to total loss oiling and the inherent inefficiencies of a valve-less design.

2 stroke diesels, though, have been around for quite a while and differ from their gasoline counterparts in that they do have exhaust valves (as well as intake ports similar to a gasoline two stroke). They also have a blower, which forces air through the intake ports when the piston is at the bottom of its stroke, and clears exhaust through the valves in the cylinder head. This design allows the engine to run a lot cleaner than a gasoline 2 stroke, and I’ve often wondered why they aren’t more common than they are (typically they’re only used in large vehicles like trains, buses, ships, etc.)

Milan July 28, 2010 at 7:13 pm

Do you think the article is correct in arguing that improved two stroke engines could allow cars to get 60mpg (3.9 litres/100km)?

Tristan July 28, 2010 at 9:19 pm

The new technology introduced by this article is exciting, and a good event for the reasons Milan points out above.

However, the article is poorly researched, and gives the impression that the last advancement in 2 stroke engines was loop charging (or as they call it, “loop scavenging”. My father’s 1975 Mercury Outboard had loop-charge – and it was quite powerful (150hp from a 1.5 liter engine would have been impossible in a 4 stroke design during the 70s, and still difficult today).

However, many important technological innovations have occurred in 2 stroke motors since the 70s. One important innovation was oil-injection. This meant the correct amount of oil for the moment could be injected, rather than a static amount of oil be mixed in with the fuel. While there remains the problem of “total loss” of lubricant, the amount of oil consumed is reduced significantly in oil injection engines.

But, the most important innovation in 2 stroke technology up until the variable-compression technology discussed in the above cited article is the advent of direct-injection in two stroke engines. This was introduced in response to California’s strict emissions regulations of the 1990s, which threatened to ban 2 stroke outboards from boats in the state – except Mercury developed DFI, a direct fuel injected two stroke engine which met the “impossible” standards.

Now, direct injection in two stroke outboards is normal. I believe Mercury calls it their “Optimax” system, other firms have different names.

Matt July 28, 2010 at 11:44 pm

Do you think the article is correct in arguing that improved two stroke engines could allow cars to get 60mpg (3.9 litres/100km)?

That’s sort of a general question. There are already cars that achieve that mileage. Could a 2 stroke engine do so? It probably depends on the car and the engine.

except Mercury developed DFI, a direct fuel injected two stroke engine which met the “impossible” standards.

I wonder if the next round of emissions laws, whenever that happens to be, doesn’t threaten the two stroke again. Although like you mention the new engines are vastly improved, they still can’t beat a 4 stroke for cleanliness and fuel economy. They still spit out a lot of oil into waterways. Of course they do have advantages: weight, durability, and powerband suited to a marine environment. Having said that, at least one marine manufacture, Honda, has gone all 4 stroke. Even their smallest engine, a 2HP unit, is 4 stroke.

Tristan July 28, 2010 at 11:57 pm

As far as I know, Honda has never produced a 2-stroke outboard. This seems to have more to do with the personal beliefs of Honda’s founder than anything else:

“Since the release of its first outboard engine, the GB30, in 1964, Honda has committed itself to the development and production of environmentally-responsible 4-stroke outboard engines. Honda’s founder, Soichiro Honda, strongly believed that discharging oil into the water was bad for everyone ? the water itself, the fish that lived in the water, and the rice which grew in the water ? and took on the long-term challenge of overcoming the difficulties of size, weight and lubrication inherent in the development of a 4-stroke outboard engine.”

Matt July 29, 2010 at 12:08 am

I knew they were using what were essentially minivan engines in their larger units, but I was under the impression their smaller units, (9.9s, etc) had been 2 strokes at one point. Thanks for the info.

Tristan July 29, 2010 at 12:40 am

I can’t say for certain that honda has never produced a 2 stroke outboard. Certainly they have produced two stroke everything else!

Arslan February 11, 2011 at 4:34 pm

Could anyone please give me some information about MOST RECENT DEVELOPMENTS in Two-stroke engines and why car manufacturers have renewed interest in two-stroke engines. When we’ll be seeing cars running by two-stroke engines?

I’ll be very thankful in this regard.

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