Diesel engine warm-up

[Timleech]

I am not sure where you are getting mixed up but in simple terms, there is only one basic type of governor. It governs the speed by regulating the fuel supplied to the cylinder for any given speed/power requirement. The speed can be varied where the governor is connected to an accelerator pedal (as in a car) or a hand speed regulator (as on a boat or certain agricultural engines) - on constant speed industrial engines there may be an internal adjustment to set and maintain the correct speed.

 

Description here of how the governor works on the Bosch pump as used on VW diesels. Looks like a pretty straightforward bob weight governor to me

 

http://www.4crawler.com/Diesel/Governor/index.shtml

 

Tim

[nb Innisfree]

I am not sure where you are getting mixed up but in simple terms, there is only one basic type of governor. It governs the speed by regulating the fuel supplied to the cylinder for any given speed/power requirement. The speed can be varied where the governor is connected to an accelerator pedal (as in a car) or a hand speed regulator (as on a boat or certain agricultural engines) - on constant speed industrial engines there may be an internal adjustment to set and maintain the correct speed.

 

On modern engines, an electronic or computer controlled device acts as the governor but it still does exactly the same job.

 

You can stall a diesel engine if the load is significantly increased at low rpm but the governor will try to keep it going and this is exactly what happens when I get something nasty wrapped round the prop - my engine doesn't slow down but the normally quiet exhaust suddenly starts to bark and the engine gets very hot very quickly!

 

 

 

In a modern car or boat engine (as I said earlier I have no experience of trad engines) when load is applied engine will slow down, gov will not alter throttle setting but lower centrifugal force will alter fuel flow, without altering throttle setting, to maintain correct fuel injection for reduced rpm

 

If I start my boat engine and set speed at say 1500rpm and then excite my alternator, the load from that alt will slow my engine to approx 1400rpm (approx 5bhp load) if I had as you say a gov which maintained rpm then it would increase rpm back to 1500rpm, but it doesn't. To get it back to 1500rpm I have to open the throttle lever a bit more. If I had a speed gov as on tractor/generator it would bring rpm back to 1500 without having to reset lever

[Timleech]

In a modern car or boat engine (as I said earlier I have no experience of trad engines) when load is applied engine will slow down, gov will not alter throttle setting but lower centrifugal force will alter fuel flow, without altering throttle setting, to maintain correct fuel injection for reduced rpm

 

If I start my boat engine and set speed at say 1500rpm and then excite my alternator, the load from that alt will slow my engine to approx 1400rpm (approx 5bhp load) if I had as you say a gov which maintained rpm then it would increase rpm back to 1500rpm, but it doesn't. To get it back to 1500rpm I have to open the throttle lever a bit more. If I had a speed gov as on tractor/generator it would bring rpm back to 1500 without having to reset lever

 

There could be another reason for that, in that your tacho is probably driven from the alternator. Exciting the alternator will increase the load on the belt and cause a degree of belt slip or creep so that the alternator (and therefore tacho) will run a little slower.

 

Tim

[nb Innisfree]

There could be another reason for that, in that your tacho is probably driven from the alternator. Exciting the alternator will increase the load on the belt and cause a degree of belt slip or creep so that the alternator (and therefore tacho) will run a little slower.

 

Tim

 

 

Engine definitely slows down, it can be clearly heard, that is why when charging batteries and alternator load gradually decreases engine gradually speeds up. No slip on twin alt belts, alt gives full output on excitation. Tacho runs of 12v engine alt, 24v alt is dedicated to leisure batts. No increase in load on tacho alt when 24v alt is excited

Edited July 4, 2009 by nb Innisfree

[nb Innisfree]

Obviously they do not mean 'throttle' in the correct sense. It is a shame that they do not use the correct terminology but so many words in the English language seem to have taken on meanings that have little relationship to what was intended.

 

Personally I'd like to 'throttle' these aberrations

 

Yes but you know what we all mean in the context of what we are discussing. When I say throttle, read, speed regulator, or perhaps SR might be better if we agree on that? (if this debate keeps going)

[Timleech]

Yes but you know what we all mean in the context of what we are discussing. When I say throttle, read, speed regulator, or perhaps SR might be better if we agree on that? (if this debate keeps going)

 

That's not what you said earlier in the thread

 

Tim

[nb Innisfree]

That's not what you said earlier in the thread

 

Tim

 

Isn't it? I can't recall, can you quote me ?

[NB Alnwick]

Engine definitely slows down, it can be clearly heard, that is why when charging batteries and alternator load gradually decreases engine gradually speeds up. No slip on twin alt belts, alt gives full output on excitation. Tacho runs of 12v engine alt, 24v alt is dedicated to leisure batts. No increase in load on tacho alt when 24v alt is excited

 

With most mechanical governors, there will be a slight decrease in speed when the load is increased.

Between 2.5% and 10% is pretty well the normal range and, as I said earlier, it is possible to stall a diesel engine if an excessive load is applied at low rpm. If the engine slows significantly, as described above, the most likely explanations would be excessive load beyond the engines power range or a worn or faulty governor.

[Timleech]

Isn't it? I can't recall, can you quote me ?

 

Yes as I said a diesel is an unthrottled i.c. engine i.e, no throttle, part of the reason why petrol engines can close the economy gap with diesell on a fast run, the petrol flat out is unthrottled. If you have a fixed throtte setting on diesel and the load increases then rpm will decrease, or vica versa, same as petrol.

 

Tim

[nb Innisfree]

With most mechanical governors, there will be a slight decrease in speed when the load is increased.

Between 2.5% and 10% is pretty well the normal range and, as I said earlier, it is possible to stall a diesel engine if an excessive load is applied at low rpm. If the engine slows significantly, as described above, the most likely explanations would be excessive load beyond the engines power range or a worn or faulty governor.

 

I don't consider the load excessive considering it is 100 amp @24v alternator which according to alt specs is in the region of 6bhp, about the same as prop at that speed. Any modern canal boat engine be it Lister Petter, Kubota,etc. will slow down when any load is applied, the gov won't increase speed untill speed controller (hand lever?) is increased, my engine is in perfect working order, has completed over 2000hrs from new and performance hasn't altered at all in 4 years

 

Another example. Take a petrol lawnmower, to maintain rpm the normal throttle linkage has to be fitted with a speed governor, normally in the form of an air inlet controlled flap which overrides the speed setting lever and open or closes the throttle therefore continually adjusting and maintaining speed with minimum variation. If a diesel engine is fitted the 'throttle' or fuel governor has to be overriden in the same way, it won't work with a standard fuel pump governor.

 

Looking at a tractor diesel engine, if you open the fuel pump lever directly by hand the engine behaves the same as a car engine, fuel injector pump has a governor inside functioning as normal. On the end of the injector pump, fixed to the pump shaft is an external centrifugal governor. When speed lever is opened it pulls on fuel pump lever via a spring, this spring allows the fuel pump lever to be varied by the external governor independantly of speed lever setting. If load, say, decreases, engine rpm will increase, external governor bob weights will, due to increased centrifugal force push the fuel pump lever back thereby reducing speed leaving the spring connected speed lever untouched. You therefore have two governors, one inside the fuel injector pump as normal and a second external one. That is the principle of a constant speed governor.

 

This mechanical system is probably obsolete nowadays all done electronically I would think, Gibbo's area I think .

Edited July 4, 2009 by nb Innisfree

[PhilR]

Tim

 

rofl - just enjoy a quiet drink Tim - and be careful you don't get throttled on the way home

[nb Innisfree]

Tim

 

I am saying we know what we are referring to when using the word throttle in the context of this thread, not what I said, but what I meant.

[NB Alnwick]

>snipped<

Looking at a tractor diesel engine, if you open the fuel pump lever directly by hand the engine behaves the same as a car engine, fuel injector pump has a governor inside functioning as normal. On the end of the injector pump, fixed to the pump shaft is an external centrifugal governor. When speed lever is opened it pulls on fuel pump lever via a spring, this spring allows the fuel pump lever to be varied by the external governor independantly of speed lever setting. If load, say, decreases, engine rpm will increase, external governor bob weights will, due to increased centrifugal force push the fuel pump lever back thereby reducing speed leaving the spring connected speed lever untouched. You therefore have two governors, one inside the fuel injector pump as normal and a second external one. That is the principle of a constant speed governor.

 

This mechanical system is probably obsolete nowadays all done electronically I would think, Gibbo's area I think .

 

I think you may be getting mixed up somewhere. I do not know of any diesel engines that need two governors carrying out separate tasks - one managing the engine speed whilst the other manages fuel flow.

 

The only type of governor fitted to a diesel engine is one that both measures engine speed and regulates the fuel flow accordingly. If the speed drops (usually due to increased load) the governor gradually increases the fuel flow until the desired engine speed is achieved.

 

On vehicles, marine engines and most agricultural applications the engine speed can be varied through a pedal or lever that is linked to the governor - there is no throttle as such. This works by altering or adjusting the governor setting so that the engine speed increases or decreases accordingly. Under extreme loads (such as a car or truck engine accelerating) it may take some time for the speed to build up and often excess fuel will be consumed causing black smoke. This is less obvious on modern engines where the governor actions are performed electronically so that the acceleration is gradual and controlled even if you 'put your foot right down'.

 

If, as you have suggested, there are applications where a governor is combined with the fuel injection pump then this is all that is necessary. There will not be a separate governor in addition.

 

Because of the way that a diesel engine functions, a governor is always necessary to monitor and regulate fuel flow - that is what it is there for.

[nb Innisfree]

I think you may be getting mixed up somewhere. I do not know of any diesel engines that need two governors carrying out separate tasks - one managing the engine speed whilst the other manages fuel flow.

 

The only type of governor fitted to a diesel engine is one that both measures engine speed and regulates the fuel flow accordingly. If the speed drops (usually due to increased load) the governor gradually increases the fuel flow until the desired engine speed is achieved.

 

On vehicles, marine engines and most agricultural applications the engine speed can be varied through a pedal or lever that is linked to the governor - there is no throttle as such. This works by altering or adjusting the governor setting so that the engine speed increases or decreases accordingly. Under extreme loads (such as a car or truck engine accelerating) it may take some time for the speed to build up and often excess fuel will be consumed causing black smoke. This is less obvious on modern engines where the governor actions are performed electronically so that the acceleration is gradual and controlled even if you 'put your foot right down'.

 

If, as you have suggested, there are applications where a governor is combined with the fuel injection pump then this is all that is necessary. There will not be a separate governor in addition.

 

Because of the way that a diesel engine functions, a governor is always necessary to monitor and regulate fuel flow - that is what it is there for.

 

We need to go back to the origin of our discussion in that you queried someone who when trying slip away quietly in the morning was forced to put extra revs on to overcome vibration caused by a cold engine and an alternator under heavy load, you said the governor should keep the revs constant irrespective of load, my original point is that any boat with a modern engine placed under load will slow down and to reinstate that engine speed is not automatic, you have increase to revs manually via engine speed lever, all boats I have experienced behave this way.

Edited July 5, 2009 by nb Innisfree

[colin stone]

my original point is that any boat with a modern engine placed under load will slow down and to reinstate that engine speed is not automatic, you have increase to revs manually via engine speed lever, all boats I have experienced behave this way.

 

???? - not if the governor is working correctly. As load comes on engine, the governor will detect the revs drop slightly and open the fuel rack to increase fuelling to the engine and increase speed.

 

And for the original question - on a modern engine - start up, drive off and do not use high loads until engine and its oil are fully warmed through. On an old engine it might require all sorts of tickling to get going.

Edited July 5, 2009 by colin stone

[MoominPapa]

???? - not if the governor is working correctly. As load comes on engine, the governor will detect the revs drop slightly and open the fuel rack to increase fuelling to the engine and increase speed.

 

Help! I'm turning into chris w here, jumping up and down and considering sending in pages of maths!

 

As I've explained twice already, if the governor is centrifugal weights balanced against a spring, that can't be true. Yes, when the revs drop the centrifugal weights will pull less and the spring will open the fuel racks more, but it can't open them enough to get back to the original revs, it must balance out at lower revs to keep the fuel racks more open. If the revs returned to what they were orignally, the fuel rack would also return to the original position which isn't possible with a heavier load.

 

This is in line with what people have reported here and what I see. And increase in load results in more fuel flow and a reduction in revs.

 

MP.

[Timleech]

Help! I'm turning into chris w here, jumping up and down and considering sending in pages of maths!

 

As I've explained twice already, if the governor is centrifugal weights balanced against a spring, that can't be true. Yes, when the revs drop the centrifugal weights will pull less and the spring will open the fuel racks more, but it can't open them enough to get back to the original revs, it must balance out at lower revs to keep the fuel racks more open. If the revs returned to what they were orignally, the fuel rack would also return to the original position which isn't possible with a heavier load.

 

This is in line with what people have reported here and what I see. And increase in load results in more fuel flow and a reduction in revs.

 

MP.

 

As I understand it, the governor can readily be designed to give no drop in speed when the load is increased but that is liable to lead to instability (hunting), so most engine governors are arranged so that there is a slight drop in speed when extra load is applied because that is a simple route to stability. In vehicle engines etc, where a drop in speed is unimportant it makes the design simpler (stability easier to obtain), but the principles are still the same.

 

Tim

Edited July 5, 2009 by Timleech

[Iain_S]

As I understand it, the governor can readily be designed to give no drop in speed when the load is increased but that is liable to lead to instability (hunting), so most engine governors are arranged so that there is a slight drop in speed when extra load is applied because that is a simple route to stability. In vehicle engines etc, where a drop in speed is unimportant it makes the design simpler (stability easier to obtain), but the principles are still the same.

 

Tim

 

As per my Land Rover under light load : if. in first gear low. the clutch is let in, the engine initially slows, but then speeds up, causing acceleration for a second or so, before slowing again to a speed slightly ABOVE idle. And all without touching the accerator

 

Iain

[nb Innisfree]

Help! I'm turning into chris w here, jumping up and down and considering sending in pages of maths!

 

As I've explained twice already, if the governor is centrifugal weights balanced against a spring, that can't be true. Yes, when the revs drop the centrifugal weights will pull less and the spring will open the fuel racks more, but it can't open them enough to get back to the original revs, it must balance out at lower revs to keep the fuel racks more open. If the revs returned to what they were orignally, the fuel rack would also return to the original position which isn't possible with a heavier load.

 

This is in line with what people have reported here and what I see. And increase in load results in more fuel flow and a reduction in revs.

 

MP.

 

Hallelujah! absolutely spot on, same for car and canal boat.

 

Thanks

 

 

As per my Land Rover under light load : if. in first gear low. the clutch is let in, the engine initially slows, but then speeds up, causing acceleration for a second or so, before slowing again to a speed slightly ABOVE idle. And all without touching the accerator

 

Iain

 

Agree with that, but in speeds above tickover the other argument holds true. If driving on level road with steady accellerator setting then car starts to climb hill (load being applied) vehicle will slow down requiring more accellerator to return to original speed.

[NB Alnwick]

>snipped<

 

This is in line with what people have reported here and what I see. And increase in load results in more fuel flow and a reduction in revs.

 

MP.

 

Some mechanical governors may be designed to do this - in which case, the speed reduction will be no more than minimal in order to prevent hunting. Any major reduction in engine speed for a given setting on the speed regulator (lever) or accelerator pedal is indicative of a worn governor and/or worn linkages.

 

A decent hydraulic governor designed for marine engines is capable of maintaining a constant speed at any given setting of the control lever.

[NB Alnwick]

Agree with that, but in speeds above tickover the other argument holds true. If driving on level road with steady accellerator setting then car starts to climb hill (load being applied) vehicle will slow down requiring more accellerator to return to original speed.

 

True of a petrol engine certainly but our modern diesel car is capable of maintaining a steady engine speed until such time as the load is too much for it and it is time to select a lower gear. As I said earlier, modern automotive diesel engines have complex electronic controls that manage the engine and it is possible to stall the engine (rather than kick out clouds of black smoke) if too much load is applied at low speed.

[MoominPapa]

Some mechanical governors may be designed to do this - in which case, the speed reduction will be no more than minimal in order to prevent hunting. Any major reduction in engine speed for a given setting on the speed regulator (lever) or accelerator pedal is indicative of a worn governor and/or worn linkages.

 

A decent hydraulic governor designed for marine engines is capable of maintaining a constant speed at any given setting of the control lever.

Yes, my explanation only holds true for a simple mechanical governor which has a spring and bob-weights opposing each other. It's not just a question of "designed" to do it, it's inherent in the nature of the beast. There's no way to design such a governor which doesn't exhibit this behaviour, though the degree must depend on the rate of the spring and I suspect, as you say, that a governor designed to minimise the rev-reduction is more prone to hunting and vice-versa.

 

I don't doubt that that it's possible to design a governor which doesn't exhibit this behaviour, I could sketch an electronic system that won't, and the all-knowing computer in modern common-rail diesels certainly won't. I believe you that a hydraulic governor can be built that way. But for a simple spring and bob-weight governor, it will always sag under load.

 

I know that the governor in the FR and JP is just a spring and bob-weights, but even the insides of a BMC injection pump/distributor may well be more complex. I've never taken one apart to see.

 

MP.

Edited July 6, 2009 by MoominPapa

[Sir Nibble]

For the drooping under load effect of a centrifugal governor, just see any big, old, gen set where frequency (speed) always has to be adjusted after load is applied. Electronic governors usually work to around +/- 0.001% no load to full load. You cannot make a centrifugal governor that doesn't droop.

[Timleech]

Yes, my explanation only holds true for a simple mechanical governor which has a spring and bob-weights opposing each other. It's not just a question of "designed" to do it, it's inherent in the nature of the beast. There's no way to design such a governor which doesn't exhibit this behaviour, though the degree must depend on the rate of the spring and I suspect, as you say, that a governor design to minimise the rev-reduction is more prone to hunting and vice-versa.

 

I don't doubt that that it's possible to design a governor which doesn't exhibit this behaviour, I could sketch an electronic system that won't, and the all-knowing computer in modern common-rail diesels certainly won't. I believe you that a hydraulic governor can be built that way. But for a simple spring and bob-weight governor, it will always sag under load.

 

I know that the governor in the FR and JP is just a spring and bob-weights, but even the insides of a BMC injection pump/distributor may well be more complex. I've never taken one apart to see.

 

MP.

 

If I have an hour or so to spare this evening (after fixing the washing machine!) I'll see whether it's viable to scan and post a couple of pages on basic mechanical governor design. MP should find it interesting, even if noone else does

 

Just to muddy the waters a bit, CAV used to make (I expect others did too, if it was any good) a 'minimum and maximum' governor for motor vehicle engines. This controlled the idling speed and limited the top speed, at other times the fuel rack was contolled directly by the accelerator pedal.

Maybe this style became widespread for vehicle engines, I really don't know, but it's really only suitable for road vehicles. Industrial and tractor engines, which form the basis of most canal boat engines now, need more of a 'proper' governor.

 

Tim

[Proper Job]

Just to muddy the waters a bit, CAV used to make (I expect others did too, if it was any good) a 'minimum and maximum' governor for motor vehicle engines. This controlled the idling speed and limited the top speed, at other times the fuel rack was contolled directly by the accelerator pedal.

Maybe this style became widespread for vehicle engines, I really don't know, but it's really only suitable for road vehicles. Industrial and tractor engines, which form the basis of most canal boat engines now, need more of a 'proper' governor.

 

Tim

I think you're spot on there Tim.

 

Modern vehicles have complex engine management systems to control idle speed and rev limiters. If you want to maintain a constant road speed thereafter you either manually depress or let off the accelerator, or, engage the cruise control.