In article <792abaf9.0312230912.1668e74c@posting.google.com>,
dbohara@mindspring.com says...
Why do diesels produce so much soot? Is it the diesel cycle or the
fuel? BTW, Europe has far more diesels than the US because they are
more fuel efficient, so should we consider that they are more to blame
for global warming than the US as far as soot goes?
In an unregulated diesel engine, obtaining maximum power requires excess
fuel in the cylinder in order to "burn" all the oxygen out of the mix.
The excess fuel ends up as soot. In a spark ignition, gasoline engine, at
max power, the unburned fuel exits the cylinder as an invisible gas or as
partially combusted CO. It's relatively easy to add a catalytic converter
to a gasoline engine to burn the CO and unburned hydrocarbons, by adding
more air to the exhaust downstream of the cylinder. With a diesel, the
catylitic converters don't work as well with soot, ie, carbon particles.
Add computer controlled fuel injection to either type of engine reduces
the excess fuel at the source by metering the fuel more pecisely and by
atomizing the fuel more throrughly. However, oxides of nitrogen are
also a problem, particularly with the diesel, as the compression/expansion
ratios are greater for this type of engine.
One should also note that it's the high expansion ratios which produce
the higher conversion efficiency of the diesel versis the gasoline engine.
This is especially true at idle and low power settings, since the diesel
operates with a full charge of air in the cylinder, whereas the gasoline
engine at part throttle only admits a partial charge of air mixed with fuel.
I think you will find that the latest diesel engins technology produceds
almost no soot emissions, although I don't have data to support that thought.
