[Gasification] Prime movers -- The Slow Go diesel concept

[AJH]

On Wed, 2 Aug 2006 11:14:50 -0700, jim mason wrote:

>yes, a slower rpm at high load will give more time for blowby.  but
>many marine and slow speed diesels have survived well with this.
>likely depends on ring configuration.  halving the desired running rpm
>is likely to not exceed the design parameters.

My understanding of this is that the power band of a diesel tended to
be rather narrow, hence many gears. I think turbocharging and flatter
torque curves has got around this with modern high speed diesels
(which work nearer to Otto cycle but retaining the higher inherent
thermodynamic efficiency of working on a full gas charge.

The killer with running an engine lightly loaded and at high idle is
that the operating temperatures get low enough for compounds to
condense in the bore, causing bore glazing. This means the rings don't
bed into the bore properly and you get both blow by and lubricating
oil entering the combustion chamber.
>
>yes, having all combustion happen at the top of the stroke does create
>the highest load on the motor, but also the highest efficiency, as the
>entire expansion is mined.  the closer a diesel gets to the otto
>cycle, the more efficient it is.

Yes this is my understanding but that tends to mean a constant high
power, which doesn't suit many, even stationary applications.
>
>while we are complicating peter's project, maybe we should encourage
>him to add a pyrometer to monitor exhaust gas temps, 

Many large tractors used to have exhaust gas temperature meters just
so and to choose a gear that optimised engine performance (i.e. kept
it running at designed power).


>as well as a
>oxygen sensor so that fuel consumption and exhaust gas temps can be
>plotted against mixture.

There I suspect you will have a problem with most lambda sensors as
they tend to work in a narrow band. Even at full power a diesel is
operating lean of stoichiometric.

I've a more expensive titania based exhaust gas probe that may give a
more linear output but it is based on a resistance change rather than
voltage generation, I think.

If a liquid fuel is readily available then I would stick with a diesel
cycle, if it's a gaseous fuel that requires premixing then I'd stick
with spark ignition but look at asynchronous running.

It's plain there are many modes of running to optimise fuel
conversion. I'm surprised a manufacture does not publish a full set of
curves for specific fuel consumption at varying loads and engine
speeds, hopefully Ken will be able to log these for his set up.

AJH