Oil & Fuel Gas vs Diesel PTO HP

[slowzuki]

Two other things too, diesels then to have more rotating mass including bigger flywheel. This means when small surges of power demand as smoothed out better.

The other thing is a diesel is speed governed directly via the injection pump while a gas engine on a tractor is speed governed via the throttle plate. In any case a diesel with good torque rise can respond to loads quicker and avoid being dragged down.

Some diesels can temporarily exceed its rated output when doing this. Gas engines can't usually exceed their rated output. Only some much fuel they can draw in no matter what.

 

[MMM]

I tend to think a lot of it has to do with volatility of gas. Higher cyl pressures from heavy loads on crankshaft are more favorable to diesel engine, where gas under same pressure will pre ignite, heat up comb chamber, and make predetonation worse. hence the knock of a gasser under heavy load. My observations from owning both fuel type tractors.

 

[Charlie_in_TX]

</font><font color="blue" class="small">( I’m going to agree with most/all of what has been said, but want to add my thoughts for a very specific situation.

If both a gas and diesel engine running the same RPM (ex. PTO speed 2600) and have 25 HP available, then both are putting out (at that speed) the same torque. After all, HP is just torque times RPM.

So, if you had a 25 HP load on the PTO, and that load never when up or down, then the engines would feel like the same power.

But, in the real world loads are always changing, and many times we are not running the engine at PTO speed. That is where the differences are easily seen. A diesel has a flatter (or even negative sloping) torque curve, and a gas engine has a positive sloping torque curve.

The bottom line is that in real world use, where you run the tractors engine at 25% to 100% PTO speed depending on the task, a diesel is much better suited for the job.

- Eric
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(finger pointing to nose) You hit it on the head. If the PTO is turning 540rpm and has 25hp there will be the same amount of torque. HP = torque * speed * a constant (that depends on units for torque and speed). The advantage of the diesels is when they are loaded and slow down. Say the load slows the PTO by 10% (540 to 486 rpm). The motor connected will also slow 10%. A diesel motor that goes from 3000rpm to 2700rpm will likely see a torque increase and keep the hp near the same. A gas motor will loose torque and far more hp than the diesel.

 

[Dachshund]

Well - even though the diesel has the advantage under load - I'll stick with a gasser. Used to have a diesel - got tired of fixing it. It's just my personnal preference, but I like the gassers. Diesel exhaust also messes with my siniuses, so I stay away from it!