<div class='quotetop'>QUOTE (BarryMachine @ Feb 11 2008, 04:53 AM)
<{POST_SNAPBACK}><div class='quotemain'>sorry guys .... that article was a lot of "hoohickey and bunkum", engines have long been a passion of mine so I hate to see "myths" produced ....
2 strokes just don't have a place in a high performance but fuel efficient, and environmentally friendly, world.
Admittedly, 2-stroke DI is currently only being used to full potential in marine environments at the moment, but it cannot be said yet that engineering development of this technology for high performance
IS a dead end.
The mechanical efficiency of a two stroke is higher than a four stroke since there is no valve gear etc. If the engine is designed to run at a set speed and throttle setting it can be even better than the efficiency of a four stroke. This may be why they are used on outboards where revs and throttle are held constant for long periods of time. The other issues with outboards are weight, size and simplicity, areas where two strokes have a distinct advantage.
When comparing equal displacement engines, 4-strokes develop significantly less torque at the same RPM than 2-strokes due to 2-strokes having twice as many power strokes per revolution.
As far as emissions are concerned, 4-stroke models tend to have a slight advantage in the hydrocarbons (HC) category, while 2-stroke direct injection models tend to have the advantage in the carbon monoxide (CO) and nitrogen oxides (NOx) categories
Conventional two-strokes carry a fuel penalty because the exhaust port is partially uncovered by the piston as it moves up on its compression stroke. So some of the intake charge is pushed out the exhaust along with the remains of the previous cycle's burnt gases. Emissions take a hit for the same reason.
With DI, the exhaust port is completely covered by the piston before the fuel is squirted directly into the combustion chamber, so no fuel is wasted.
You stated in a previous post that DI in 2-strokes was not much different than what old hot bulb oil engines ran. Yes, both directly inject fuel into a combustion chamber, but it is only relatively recently that this has been done with gasoline engines. The hot bulb diesel used mechanical pump "solid" injection, whereas modern gas injection uses air assisted very high pressure injection with a stratified charge.
(inside joke)
