Diesel engine fuel systems

[kenimpzoom]

I keep hearing that diesels dont have a throtle.<br /><br />But the only diesel I have ever worked on was a small truck Isuzu diesel and it did have a throttle body.<br /><br />Here is a pic :<br /> http://www.geocities.com/kenimpzoom/KensHomePage-Pics-Mods.html <br /><br />(You can barely see the throttle body behind the A/C compressor)<br /><br />What are the different types of diesel fuel supply systems?<br /><br />If there is no thrttle body, how is engine speed regulated?<br /><br />Ken

 

[Trent]

Re: Diesel engine fuel systems

They use a fuel injection pump. They pump fuel directly into the engine (direct fuel injection). More modern engines use a ECM to control the fuel and timing issues.

 

[QC]

Re: Diesel engine fuel systems

KIZ,<br /><br />Diesels do not have a throttle, and this is the number one reason that diesels are more efficient than spark ignited (Otto cycle) engines. Remember a throttle is the plate that opens at varying positions to restrict airflow. It is not the manifold or air intake pipe which you may be calling a throttle body. It is only a throttle body if there is a throttle in there . . .<br /><br />Diesel engine speed is regulated by a mechanical or electronic Governor. The governor "knows" what the engine RPM is and uses that along with your instructions (how far you push the governor control lever) to control power and speed. The governor control lever is probably what some would call the throttle. Pet peave of mine as again, there aint no stinkin' throttle. It even gets sillier as the linkage between a mechanical pedal and the lever is often called the throttle linkage. Whatever.<br /><br />Anyway, the governor regulates the fuel to the engine, and in the case of a diesel this alone controls power AND engine speed. If you keep putting fuel to a diesel it will keep burning it unless you restrict air OR it breaks. When a technician, who has any training whatsoever, starts a diesel engine that has had any fuel system work done on it, they stand ready with a piece of sturdy wood or other similar "plate" to cover the air intake if the engine runs away. Thiws is ofeten the only way to stop them!! <br /><br />Back to the governor . . . If the governor "sees" that the RPM has gone past a preset max, then it will restrict fuel flow to slow it down. This part of the discussion gets pretty complicated, but the answer to your question about control is in the governor and the control lever combination.

 

[kenimpzoom]

Re: Diesel engine fuel systems

Quitecat, that is a throttle body, I saw it with my own eyes, a movable plate that was controlled with the accelerator pedal.<br /><br />Ken

 

[QC]

Re: Diesel engine fuel systems

Then it is one fooked up diesel!!!! You saw the plate? Or you saw the linkage? It might have been a shutdown? Or possibly some sort of start strategy, but I would be VERY surprised if it was there to restrict airflow during normal operation.

 

[kenimpzoom]

Re: Diesel engine fuel systems

Saw the plate. You can see the linkage mounted on the firewall all the way from the left, going behind the engine and connecting to the throttle body.<br /><br />The second pic down is a better view.<br /><br />I am trying to remember, but I think the shutoff connected to the fuel injector pump. You had to pull on a cable to kill the engine.<br /><br />This is an asian spec Isuzu diesel, probably the aussies have seen tons of them.<br /><br />Ken

 

[QC]

Re: Diesel engine fuel systems

Could be EGR too, but I doubt very seriously an older Asian spec diesel woud have that . . . I have searched a bunch of parts sites looking for something that would show a better picture, but came up empty. I am VERY curious now. Let me know if you find anything out.

 

[kenimpzoom]

Re: Diesel engine fuel systems

I saw several of the same engines in a junkyard once, so it isnt a one off thing.<br /><br />Did Isuzu ever sell a diesel in theri compact trucks here in the USA?<br /><br />Just guessing, but I would say its from the 19080s<br /><br />Ken

 

[QC]

Re: Diesel engine fuel systems

Yes, there was a 2.2 in the Pup. That's where I was looking, but couldn't find any drawings . . .

 

[JB]

Re: Diesel engine fuel systems

The "engine speed/power control" on my Kubota moves a device on the injector pump to control the amount of fuel injected.<br /><br />The same was true on my three Mercedes Diesel cars ('64 and '65 190Ds and a 1968 220D). <br /><br />On none of these engines does the control regulate the amount of air admitted to the intake manifold (correctly called "throttling"). The result was essentially no manifold vacuum. That is why there was an accessory vacuum pump, crank driven, on the cars to operate the power brakes.<br /><br />Unlike throttle regulated Otto cycle gas or petrol engines that are mixture sensitive, Diesels like as much air as can be stuffed into the cylinder, no matter the amount of fuel injected. Enter the super- and turbo chargers.<br /><br />Bottom line? Correct, Diesels have no throttle. They regulate fuel delivery to unrestricted air volume to control power/speed.<br /><br />What did KIZ see in the Isuzu? Damfino.

 

[3388sam]

Re: Diesel engine fuel systems

Cats right on. With diesels you can move your throttles or pedal to max and the engines will reach their max-governed rpm and stay there.<br />Floor the gas pedal on a gas engine and stand back!<br />Plus at the cylinder pressures that diesels run, they need to inject the fuel directly into the cylinders at thousands of psi.<br />No throttle body is going to that.

 

[Darren Smith]

Re: Diesel engine fuel systems

I've worked on a few Isuzu diesels in some asphalt rollers, never saw a throttle body on a one. Although some had an adapter for the intake to filter plumbing with an emergency shutdown that blocks all the air, but it was open when the engine was running, and closed in the event of emergency. Very interesting.<br />As said before, diesels (evidently generally) do not use a throttle body to controll engine speed. It is done by the fuel pump or the governor. Learn something new everday!

 

[Darren Smith]

Re: Diesel engine fuel systems

P.S. I would like to see more pictures of that!

 

[JRJ]

Re: Diesel engine fuel systems

The only diesel "run-aways" I am aware of were old Detroit 2-cycle engines that could malfuntion and injest crankcase oil. The oil worked as fuel and the engine could wind up, even without fuel feed, to overspeed and blowup. The engines I was around had a manual emergency shutdown control that shut off the air supply. Once the emergency was pulled, a manual re-set had to be done under the hood before the engine would re-start. A common prank was to pull a rookies emergency

 

[QC]

Re: Diesel engine fuel systems

JRJ,<br /><br />You are right about the 2 Cycles, but 4 Cycles can and do run away on their own oil and fairly often, but I was actually refering to fuel which can take either of them down very hard . An example of an oil runaway in a 4 Cycle is a failure of the turbo oil seal. The worst examples happen when over time the turbo continues to fill the Air-to-Air aftercooler with oil. It can hold a lot, and as soon as the amount of boost from the turbo starts pushing that oil across to the intake they can go sky high. Technicians are now instructed to pull an intake pipe off before they move a truck into the shop if they suspect an oil seal failure.<br /><br />KA,<br /><br />it sounds like Isuzu uses an air shutoff in some applications and that is what KIZ is seeing. Maybe they use both fuel and air shut-offs for safety . . .<br /><br />I just want to caution all that using the word throttle-body is where the trouble starts . . . Diesels simply do not and cannot inject fuel into the intake air. In a diesel, ignition timing is controlled by fuel injection. If the fuel is mixed in the air before the cylinder, then there is absolutely no timing control.<br /><br />Here is a diagram of a typical mechanical diesel governor. Just imagine you trying to push the fuel control to go and this thing pulls the fuel back when the engine speed starts to exceed the max. Very simpe example, but how a real basic one works.<br /><br />

 

[Peter J Fraser]

Re: Diesel engine fuel systems

Everyone is right to a degree.<br />A lot of older diesels used a throttle body valve to "control" rpm.<br />However it was a vacuum governor like the vacuum that you have in a gasoline engine.<br />At high vacuum the governor is pulled back to low fuel settings and at wide open throttle the reverse is true. There is also a mechanical governor that controls High RPM and cuts the fuel delivery to maintain safe engine speeds.<br />This combination was used with English and early Jap diesel systems with an inline injector pump up until the late 70's.<br />Modern rotary pumps eg. Bosch, Nippon Denso, Zexel, Cav are mechanical with full electronic control on Jap engines from early 90's now the norm.<br />The modern Jap diesel have a throttle plate but this is linked to pollution control EGR's and not the pump itself.<br /><br />Regards<br /><br />Peter