[sustran] 1) Motorised 2 wheelers 2)Hong Kong

[J.H. Crawford]

>I am this "low-compression" and "high compression" terminology for the 
>first time. 

Compression ratios are not directly related to the operating cycle--
it is possible to have high and low compression engines using either 
of the cycles.

>Generally, we talk about 2-stroke and 4-stroke engines for 
>motorised two wheelers (MTWs). Cars have 4-stroke engines.
>In 4-stroke engines, Hydrocarbon emissions are much lower than 2-stroke 
>engines due to beter burning of the fuel. 

And also due to the use of catalytic converters in many cases.

>In 2-stroke engines, a large
>amount of unburnt fuel is emitted into the air. 

This is not strictly correct--2-stroke Diesel engines are not
very different in this regard as compared to 4-stroke Diesels.
The valveless 2-stroke enginess commonly used in cheap, lightweight
vehicles are invariably filty in my experience.

>For the same reason, two-stroke engine have a lower CO/CO2 emissions than 
>4-storke engines. 

>Since the burning is better in 4-stoke engine, there 
>is higher emission of carbon oxides which is a byproduct of burning.

When you burn a hydrocarbon, it all eventually ends up as
water and CO2 (excepting impurities like sulfur). Some of
the emissions hang around for a while in some other form,
causing all the well-known problems, before ultimately breaking
down into water and CO2. Since 4-stroke engines are usually
considerably more efficient, they burn less fuel for a given
output, and so result in less total CO2 emission.

>It should also be noted that 4-storke engines provide better mileage.

Yes


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J.H. Crawford    Crawford Systems    joel at xs4all.nl    http://www.mokum.com/