Quote:Original post by Dmytry

Quote:Original post by LessBread

Quote:Original post by Dmytry
Ahh right. Well, i did some research, apparently India is phasing out those (gradually, starting from some cities).
Even then, i dont have any real data but wont be surprised if a car with hundreds horsepower pollutes air more than inefficient crappy motorcycle with maybe 10hp. Of course they got more motorcycles than cars... but nonetheless.
Electric bikes could be cheaper in long run, tho that depends to lifetime of battery.

A four stroke engine is cleaner than a two stroke engine. A two stroke engine burns oil by design. When a four stroke engine burns oil it indicates that the engine needs repair. A four stroke engine is larger and burns more fuel, which presumably means it produces more pollution, but here quality (rather the lack of it) trumps quantity. Two stroke engine exhaust is far worse than four stroke engine exhaust. I realize there are many variations on both engine types. My comments pertain to the common two stroke engines found on motorbikes and lawnmowers.

Two Strokes and You're Out (May 21, 2008)

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A single two-stroke engine produces pollution equivalent to that of 30 to 50 four-stroke automobiles. With roughly 100 million motorcycles in Asia—roughly half of them using two-stroke engines—that translates into as much as 2.5 billion cars’ worth of smog.
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Sounds more like bullshit created to make impression that US cars are less of a environment polluter comparing to asia and other countries. Whats that 30 to 50 times pollution equivalent? Which pollution, exactly? Could likely be clean well tuned four stroke against crappy two-stroke with crappy oil - fuel mix, running at same power.

I detect some sloppiness in that paragraph considering that Japan is a part of Asia and Japanese cars are among the cleanest (if not the cleanest) cars on the planet. That said, I don't think that paragraph stretches the truth regarding vehicle pollution in China and India. I doubt the 30 to 50 factor was derived by comparing clean well tuned four stroke engines against crappy two stroke engines. As I wrote before, finding solid comparison information was difficult.

Quote:Original post by Dmytry
From wiki btw:

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Throughout the 20th century, many small motorised devices such as chainsaws, and outboard motors were usually powered by two-stroke designs. They are popular due to their simple design (and therefore, low cost) and very high power-to-weight ratios. However, varying amounts of engine oil in traditional designs mixes with the air-fuel mixture, which significantly increases the emission of pollutants. For this reason, two-stroke engines have been replaced with four-stroke engines in many applications, though some newer two-stroke designs are as clean as four-strokes.

As I wrote before, I realize there are many variations on both engine types.

Quote:Original post by Dmytry

Quote:
Smoke on the Water (May/June 2000)

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According to estimates, a 70-horsepower (hp) two-stroke outboard emits the same mass of hydrocarbon pollution in one hour as a new car does driving 8000 kilometres.

If you thought "comparing apples to oranges" was a joke, look at comparing horsepowers to kilometers. Classic. Apples and oranges are at least both fruits.

I detect an edit here!!! [grin] That's not a comparison of horsepower and kilometers but a comparison of running times. Horsepower is noted to identify the type of engine. The article pertains to outboard motors on boats which makes it difficult to quantify the distance traveled in an hour. On the car side, 8000 km at 80 kph would require 100 hours to drive. So that comparison would have been better phrased to say that one hour of operation of a 70 hp two stroke outboard motor emitted more or less the same mass of hydrocarbon pollution as 100 hours of driving a new car. I inserted the more or less because I assumed that the entire 8000 km would be driven at 80 kph and that's not clear. It also would have been better to stipulate the type of new car.

Quote:Original post by Dmytry
Overally, i agree that two stroke makes much more smog for same power, however i disagree with exaggerations.
Additionally, on the motorcycles, limited weight and space is a problem, hence suboptimal engines, both two and four stroke.

I wouldn't say those quotes contain exaggerations. Some of them are dated so it's quite possible that they were accurate when published but are no longer accurate because of recent technological updates to two stroke engines. When it comes to pollution emissions the two stroke engines are indeed suboptimal.