How do I determine diesel starting requirements?

[Superfry]

I'm working on a weight reduction contract for a 2kW military generator. The generator uses a 4.7hp Yanmar Diesel (211cc single, air cooled).
This engine has an electric starter on it (although it is almost never used, they like the option). I believe this starter is overkill because they also use it on a 400cc diesel - and it weighs 7-8lbs. I know I can save several lbs with a gear reduction starter. My question is how do I determine the starting requirements of the engine, minimum torque/rpm, etc. I would also like to know how flywheel inertia effects starting requirements.
Any suggestions are greatly appreciated.

 

[GregLocock]

Caution: I have never messed around with starters.

Why not measure the current during a start and see what proportion of the starter's capacity you are using?

I'd guess, when starting a diesel, that a big flywheel helps to reduce the peak draw on the motor, leastways when hand cranking one I'd much rather have a big flywheel.

You need to size the starter to cope with arctic starts at a guess.

When an engine is running much of the friction is from the piston rings and valve gear - neither of which will be much smaller in a 200 cc than 400cc engine, at a rough guess.


Cheers

Greg Locock

 

[rmw]

Overcoming the initial friction and compression and getting the engine spinning is the biggest torque load on the engine. Once it gets spinning, the starter is not loaded as heavily. What is the hardest part of starting an engine with a rope starter, the initial tug, isn't it?

Take the engine, bring it up against compression in a cold, not having been run in a while (no lubrication up in the engine,) and put a torque wrench on the engine, and see how much torque it takes to break it loose.

That may give you an indication of the range you are working in.

The flywheel inertia helps you with the starting situation. Once you get the engine spinning, the flywheel trys to keep it spinning, putting less strain on the starter. However, the starter has to overcome all the friction and inertia to get it spinning.

RPM, I would just measure the rpm of the current starter, and pick a replacement starter to match that RPM. Someone who put that large starter on it put one to produce that many rpm for a reason.

I hope these comments aid you in your quest.

rmw

 

[PJGD]

For starting a compression ignition engine, the instantaneous speed over TDC is a critical parameter, hence the desire for a substantial flywheel. There is no point in having a high average rotational speed, but it slows down significantly as it goes over compression TDC.

PJGD

 

[EdDanzer]

We use a 10 hp Yanmar air cooled diesel in a pull through delimber we make. These engines can be difficult to start in cold weather, under 32° F. In our application the engine drives a hydraulic pump making cold weather starting even more difficult. We have even built gear drive starters for additional starting power. The problem with this engine is the fuel system does not flow adequate fuel to start in cold weather. The cranking speed is not as important as the fuel temperature. Having spent several thousand dollars on starting aids and starters, the most for the least is our fuel line heater that clamps onto the injector line by the injection pump

http://www.danzcoinc.com/html/automotive.html

. You could experiment with a smaller starter from a 1 cylinder gas engine but adapting the starter nose and bendix is no fun.