John H
Post Posted: Sat Jun 21, 2003 11:45 am
 Subject: ahhh - you'd be bored - it develops peak power at only 102rpm!

...which leads me to wonder how slowly an engine can turn before it stalls - i guess there's one whole heap of inertia in that thing to keep it turning and relatively little friction compared to a little motor like our 250.

I've been in the cab of a 1952 vintage railway loco firing up - 16 cylinders each of 567cid capacity (9072cid total) - it was actually rather dull. Whirr, then hum. No fun at all!
Post Posted: Fri Jun 20, 2003 9:46 pm
 Subject: Anyone watch the Discovery bit on Hyundai motor corp?

I am not sure if it is a deisel engine or not, but it is a combustion engine, completely manufactured and used in their largest tanker ships, it puts out 95,000 hp. Anyway, the motor is 4 stories tall.
Post Posted: Fri Jun 20, 2003 9:08 pm
 Subject: Thermodynamics, the short lesson

A parameter that is used to describe the efficiency of a reciprocating piston engine is the Mean Effective Pressure (MEP). MEP is the theoretical constant pressure, if it acted on the piston during the power stroke, that would produce the same net work that is actually produced in the cycle. You can increase this MEP to increase the thermal efficiency of the engine, look it up and you'll learn some techniques for increasing MEP.

Another thing that is useful to know is that Thermal Efficiency increases with increasing compression ratio. This is why diesel engines are more efficient. This increase in efficiency however is limited by the cutoff ratio of your piston cylinder assembly. The cutoff ratio is the volume in the cylinder just after ignition divded by the volume in the cylinder just after compression and before ignition. The smaller the cutoff ratio, the higher the engine efficiency. The compression ratio increase is also limited by "autoignition", which is fuel combusting under compression rather than spark in spark-ignition engines. The upper limit is needed to prevent knocking.

Here are some graphs to help you see the relations I just discussed. Rc is the cutoff ratio. Please remember these are curves that do not account for engine friction. That is why the curves seem high, friction is what brings them way down to the efficiencies we know and hate.

I won't go into crazy amounts of more detail from a thermodynamics perspective, but hopefully you know a little more about engines now. If you want to know more about what YOU can actually do to increase the efficiency, a simple google search will give you thousands of ideas. The best thing you can do to increase efficiency is reduce friction inside your engine, but that's not so easy. For those of you that care though, the Ninjette has a thermal efficiency of 20.4%, not too bad really. I am sure you can increase it if you want though.
Charles Dennison
Post Posted: Fri Jun 20, 2003 8:23 pm
 Subject: Re: O/T OK, so this has nothing to do with motorcycles, but its cool

You could only wish that it would. But in 1 part that article brings up a good point. I forget how but does any one here know how to increase the thermo effeciney of the engine?
Post Posted: Fri Jun 20, 2003 8:23 pm
 Subject: HOLY SH*T !!! I would love to be there when it fires up :) (n/t)

Post Posted: Fri Jun 20, 2003 8:17 pm
 Subject: O/T OK, so this has nothing to do with motorcycles, but its cool

I think you engine lovers out there will like this though. It was a recent topic of discussion in a manufacturing class, well for reasons that are obvious when you read this site. Hope you enjoy it, and hopefully this off topic subject stays up long enough for others to see before it gets deleted.

I'd like to see if I could fit this on the EX250 somehow, think it will work?

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