Misc. diesel questions

[Bob_Trevithick]

Here's a guy, me, sitting around twiddling my thumbs and waiting for the delivery of my first "real" tractor, a JD 4300 MFWD with SyncReverser. So, with time on my jittery hands, I thought I'd ask some questions I've always wondered about.

-Can diesels be diagnosed by their exhaust, in the same way gas engines can? You know, blue means burning oil, white means too lean, etc.? What about diesels? A friend and I were following a big truck one day, and he said, oh, that engine isn't running right. It was billowing black smoke, even when the driver let off the gas to stop. I wish I had picked my friend's brain more at the time.

-I notice a lot of truckers seem to be running with no muffler, or at least it sounds like they have none. I gather they claim to get more power and better fuel economy that way. Is this true, or do they just think it's "cool" to be loud?

-With gas engines, a certain amount of back-pressure from the exhaust seems to be necessary for proper power. Is this also the case with diesels?

-With gas engines, I'm told that a short exhaust can burn the valves, since oxygen can get in there and hit the valves more easily without all the exhaust plumbing. Is this also the case with diesels?

-With gas engines, if someone wants to run straight pipes, they usually have to re-jet the engine, or so I'm told. Is this the case with diesels? Do any farmers run straight pipes to improve performance? If there are no neighbors to annoy, would this gain anything in the way of performance?

-For initial break-in, if I were to just run the engine at around 1/2 to 3/4 throttle, in a creeper gear, and clean the ruts and holes out of my driveway with the front blade, would this be considered appropriate? Or is this too much work for the break-in period? If I put on the spreader, and ran it at normal PTO speeds (2700 RPM if I recall correctly), would this be too hard on the engine during break-in?

Thanks for any thoughts!

Okay, enough rambling. Sure wish the "tractor people" would get here with my new toy! /w3tcompact/icons/smile.gif

Bob Trevithick

 

[BobinCols]

The black smoke from the semi's exhaust was from too much fuel being injected into the motor and not being burned due to a bad air filter (not enough air), a faulty injection pump or injector, or simply the driver had the fuel turned up by someone who did not know what they were doing (thinking they were going to make more power). Leave the stock exhaust sytem on your 4300. Putting a straight pipe would not make more power and would be much louder. About all semi's have turbos which quiet the exhaust with giving them power. Our compact tractors have no turbos.. On breakin-I would vary rpm's every so often and after about 1/2 hour of run time-start to work your engine by building some heat in the cylinders and getting the rings to seat. Running the spreader at 2700 would not work the engine and you wouldn't be varying the engine speed. After warming engine up good, I would do the driveway work you mentioned by making the engine work. Good luck with your new toy.

 

[JATO_RaT]

Hey Bob, the one thing that really separates the diesel and gas engines is the way they burn fuel. The gas engine always burns at a rate of 16 to 1 regardless of engine RPM (optimum) There are exceptions as the gas engine revs up and revs down. A diesel will always burn at various rates depending on RPM. From as little as 100 to 1 at idle to as much as 33 to 1 at full RPM. You can see that at idle the diesel is just barely sipping the fuel, 1 part fuel to 100 or less parts air. The reverse is also true as far as fuel rich or lean mixtures. With gasoline, a rich mixture will not overheat the engine whereas in a diesel, a rich mixture will overheat the engine. Any unburnt gases will ignite in the exhaust pipe and eventually destroy it if the condition persists. Its one of the reasons diesel trucks will use pyrometers or EGT gauges to monitor exhaust gas temps. As far as exhaust, a diesel will never suffer from a open exhaust, the less the restriction the better. I also think the less noise the better to so I make sure I keep mine quiet first. Remember, diesels have no vacuum like gas engines, the intake is wide open, they really need the air thus the reason they often get positive air from turbochargers for increased performance. If you want a bunch of info on diesels, Cummins has some interesting stuff, its where I learned about this stoichiometric (sp) process of fuel burn rates in cars and diesels. Rat...

 

[bgott]

16 to 1 is lean. The ideal A/F ratio for a gasoline engine is 14.7 to 1. A few companies have devised ways to run gasoline engines leaner such as the Honda CVCC. Those engines had a lot of added complexity to get the system to work without burning up the engine. With computerized injection and three way catalysts they want the A/F mixture to swing back and forth between rich and lean. The CO/ HC section of the cat wants to see a little extra oxygen ( lean) to fire off and the NOx section wants a little carbon monoxide ( rich) to work. I know this is way more information than you were looking for but I just got carried away! Sorry!