Nuty Professor Kinda question (diesel Gurus please respond) - PeachParts Mercedes-Benz Forum

coachgeo · #1 05-10-2003, 08:21 PM

Im wondering; I could see Overnight idleing as a solution to some of my issues but want to maximize fuel savings. There are good reasons for the overnight idleing butttt ..leaving them out for now.

Can you shut off a cylinder or two in a diesel engine by diverting fuel flow from IP to return line. Effectively making it a 2, 3 or 4 cylinder engine and still have it run smoothly ?

I know on a gas engine when you pull a spark plug boot it all the sudden dosent run right but diesels are such a different animal maybe I shouldnt assume the same to be true.

(specific engine is the 617Turbo)

The Warden · #2 05-10-2003, 08:30 PM

I don't think it would be feasible. The fuel coming out of the IP is at a very high pressure, and I don't know if the return lines (mainly rubber) could handle the direct pressure. In addition, short of custom fuel lines, I don't think you could put a valve anywhere without changing the timing. Interesting idea, though.

BTW, on a gas engine, I believe that if you pulled wires so that the opposite cylinders were firing (i.e. make a V-8 into a 4 cylinder where the cylinders were still firing every 180° of the crank), that would work. In fact, I think that someone has a V-8 gas engine that's made to do exactly that. However, I don't think that's feasible on an odd-number cylinder engine...i.e. it would be doable on a V-6 or a V-8 but not on a 5 cylinder or a 3 cylinder.

Also, extended idling for a diesel isn't all that healthy; you'd be getting unburnt fuel past the rings and into the oil, making it necessary to change the oil more often.

Just my $.02...good luck! Do you have a block heater or an oil heater?

coachgeo · #3 05-10-2003, 08:39 PM

Quote:

Originally posted by The Warden
I don't think it would be feasible. ...snip
Just my $.02...good luck! Do you have a block heater or an oil heater?

hmmmmmmm... any other comments? Big rigs diesels sit all night idleing dont they?

"Do you have a block heater or an oil heater"?... no but not a bad idea.

water heating, power generation etc. yes. A camper! Just wondering .... seems a waste to add another engine (a diesel generator) to produce power and another qizmo to produce hot water when it is avialable from da engine. .

kerry · #4 05-10-2003, 10:55 PM

Small tankless propane hot water heaters like the Paloma PH-5A are the most effective for campers since you need propane to cook unless you have a diesel stove.

kweimer · #5 05-10-2003, 11:01 PM

If you cut off one of the cylinders in a diesel engine, it is not going to run smoothly. Loosen one of the cap nuts to the injector on a diesel, and you will see what I mean. I have let a 220D idle all night while staying in a motel in upper Michigan on a very cold January night---no problem. At least nothing like the problem I would have had trying to get it started the next morning.

coachgeo · #6 05-10-2003, 11:12 PM

Quote:

Originally posted by kerry edwards
Small tankless propane hot water heaters like the Paloma PH-5A are the most effective for campers since you need propane to cook unless you have a diesel stove.

Thats the plan "diesel stove" butttttt... then again if I go to LP fumigation for hill long upgrades etc. then Im back to having some LP on board.

Would rather diesel; WVO in my case, cause that fuel will be practically free.

The Warden · #7 05-11-2003, 12:32 AM

Quote:

Originally posted by coachgeo
Big rigs diesels sit all night idleing dont they?

Some do, but that's actually a dying practice, and companies are frowning on it. The original idea was that it was cheaper to pay the fuel to let the engine idle than it was to pay for maintenance involved in starting up and shutting down engines (lubrication, starters, etc), but they've found that the reverse is true...

leathermang · #8 05-11-2003, 12:45 AM

Warden , Where does this information come from ? :

1." extended idling for a diesel isn't all that healthy;

2. you'd be getting unburnt fuel past the rings "

On running the diesel on big rigs overnight... how about to keep the Air Conditioner or heater working ?

Capt Kirk · #9 05-11-2003, 01:57 AM

I thought the whole "getting fuel past the rings" was a problem with carbeurated engines where they dumped too much fuel in at idle. With Fuel Injection the amount of fuel is more acturately metered so that only enough is put in to keep the engine running.

On these engines actual fuel has to get out of the prechamber and survive the detonation of the whole fuel-air mix before it can even think of getting past the rings.

So I don't think letting a diesel idle overnight would be a problematic idea, you might make your neighbors mad with the noise and the smell, but thats about it.

The Warden · #10 05-11-2003, 04:04 AM

The info that I've stated came from others. The should-diesels-idle debate has been hashed over numerous times on other site. In fact, before reading those arguements, I used to think that the opposite was true.

If you're interested, here's one thread and here's another.

Quote:

Originally posted by leathermang
On running the diesel on big rigs overnight... how about to keep the Air Conditioner or heater working ?

That's one other reason, although I remember reading that some new Cummins engines (the ISX, for example) have sensors to monitor the cab temperature and the engine temperature, and fire the engine off and shut it down as needed to maintain these temps. I can't remember if that was from Cummins' website or from the Diesel Progress magazine, though.

dabenz · #11 05-11-2003, 01:05 PM

You're all mostly right. Theoretically you could shut off/divert a cylinder's fuel to a can with an injector nozzle, then let that drain to the fuel tank return line. All you have to do is make sure the crank has enough momentum to make it around to the cylinders that are still in operation. However, the crank main bearings would live a tough and short life with the firing imbalance that the bearings weren't designed for.

Yes, idling (at low idle) is bad. The fuel will be metered better than a gasser, but the diesel engine is so efficient that the block/head won't stay warm. Then you get partially expanded piston rings which leads to blowby, and a cold exhaust which leads to acid rain in the exhaust system. Stop lights are ok, overnight is bad.

Yes, it used to be cheaper to run (not idle) the trucks all night. Fast enough to keep the water temp up, slow enough so that the turbo doesn't kick in. But that was when fuel was $0.60 per gallon, not today. Today's profit minded truckers use a catalytic heater (such as Webasto) for heating the engine for starting and keeping the driver warm. They use 1/10 the fuel as running the engine all night. Technology isn't there (yet) to keep the driver cool all night, so the engine runs all night just to keep the AC on.

In the end: run a diesel, don't idle it. Most of the diesel game is planning ahead. Make sure your fuel can handle the temperatures. Keep the fuel clean and dry so the glow plugs last. Use a coolant or oil heater. Etc., etc., etc.

coachgeo · #12 05-11-2003, 01:42 PM

thanks Dabenz,

Good meat to your responce. Catalytic heater.. are you meaning the diesel fired heaters of Webasto and Espar? Curiouse cause I have not heard them called catalytic heaters before, though I dont hear much talk about them anywayl.

Any other comments?

#13 05-11-2003, 03:42 PM

Actually, he's not entirely crazy. In the early days of motoring there were cars that used four cylinders until you felt the need for speed, when the other four, or eight, would kick in. Sorry I can't remember which ones. Some were real monsters, with 14 or 16 litre engines turning around 900. Those were the days!

dabenz · #14 05-11-2003, 10:44 PM

My last road truck had a Webasto. Worked great, especially after a battery was isolated just for the Webasto. They've been in Europe for years but not here because of the lower fuel costs. They do sell a unit small enough for a car or pickup engine, but they're expensive.

For emergencies, I was taught to carry charcoal, a turkey pan, and aluminum foil. Today I pack a multi-fuel backpacker's stove, a cake pan, and aluminum foil.