Crank up the boost 1.9TD ?

ohms69 · Unread post by **ohms69** » 04 Mar 2004, 20:29

Hi Guru,
Turn the fuel pressure up first, take it for a drive, check for smkoe and then djust boost until smoke dissapears. Boost alone will do nothing for performance. Forget what you know about petrol turbocharging and think adding more fuel= more power.
At 20psi it flies, and seems to have no adverse effect. it smokes no more than before, so I am well happy![:D]

Guru Meditation · Unread post by **Guru Meditation** » 04 Mar 2004, 20:31

The reasoning behind turning up the boost first was on the premise that it is over fuelled already, although if it is not then as you say more boost will not do anything for it. Gotta get my hands on a boost gauge then get started!

ActivaV6uk · Unread post by **ActivaV6uk** » 04 Mar 2004, 20:34

point 1
on a normally aspirated diesel this is correct we are talking about a system ware the air is never in the same quantity, the more air you have the higher the temp, on an normally aspirated engine the air is constant (and much less), standard diesels do get very hot generally running at the same temp regardless of fuel input (the increase in heat is only generated by friction)
Point 2
Inside the head there are swirl chambers (which let the air and fuel mix) which also stops the mixture detonating immediately that’s the reason that on the XUD it’s injected before TDC. On a direct injection it’s normally on TDC or just after.
Any one who uses an gas welder will know that the more oxygen in the mix the worse the heat it is the same in every instance. It's worth remembering that your dealing with a turbo'd not a normally aspirated diesel the more oxygen you give any explosion the hotter it gets. I’ve seen the effect of too much boost not enough fuel on an XUD engine before and the pistons were either totally destroyed or had holes in from “hotspots”. I always believe my eyes over anything I read. There are pictures some ware and one of my friends still has parts of the engine I will see what I can find…
Andy
Edit: the only point that i was trying to make was that the modifiactions need to be done sensibly its very easy to make mistakes. I'd be interested to talk about things off bord if your interested? ([email protected])

neilsxm · Unread post by **neilsxm** » 05 Mar 2004, 00:04

activav6uk
sorry mate but what you said about the turbo doesn't increase the severity of the explosion only the length of time is based on a petrol engine
turn the boost up on a diesel engine definatly increase combustion pressure by a significant amount
--neil--

neilsxm · Unread post by **neilsxm** » 05 Mar 2004, 00:15

hi all
i'm sorry but alot of you are wrong you can NOT run a diesel lean
by it's own design the air is a constant and fuel is varied to produce it's power so how do you run it lean?????
on a turbo engine it's the same but the air pressure is variable aswell
and you CANNOT damage a diesel engine by resticting it's diesel(lean?)you'll just get less power
BUT
you can seriously damage a diesel engine by over-fueling and by advancing the pump timing (more pronounced diesel knock)
--neil--

dieseldan · Unread post by **dieseldan** » 05 Mar 2004, 00:45

Hello everyone, just fancied getting in on this debate - I'm sure someone whose really knows with post the answer soon though.
I was wondering how come some of the tuners of TD's, as previously discussed in this topic, adjust the pump to the boost pressure until there is no smoke. If this is so then they must be changing the 'completeness' of combustion, smoke or no smoke, so they must then be changing the mixture rich to lean, etc. Further to this, by recently changing my dirty air filter the exhaust fumes are far less dirty and smelly and my fuel economy has increased by 3 mpg. Surely I altered the burn ratio. So does this not mean that if a clogged air filter can change the ratio then a cranked up turbo forcing 3.0 bar of air in the mix can not also do the same thing even though the pump tries to compensate by adding more fuel.
In my experience in the aviation industry you optimise the ratio of both a reciprocating and gas turbine engine by adjusting the mixture according to exhaust gas temp or turbine gas temp respectively. Where if you lean the mixture it runs hotter and vice versa.
I'd like to know the answer though.
cheers, Dan

Simon Canfer · Unread post by **Simon Canfer** » 05 Mar 2004, 01:12

Interesting thread this, one point I haven't seen mentioned is the limit that the standard intercooler imposes.
Simply by increasing the boost-compensator fuelling you can increase the power produced to quite a marked extent (I think Allard reckon up to 20%). Apparently Bosch pumps can go further than Lucas.
To get any more power than this, you need to increase boost pressure to cram more air in. However you cannot increase boost by very much before the inlet air temperature skyrockets; the last thing you want. This is where you need a bigger intercooler.
Lower inlet air temp reduces thermal stresses on the engine. So a bigger intercooler can only help. Especially when you have an XUD that likes to blow head gaskets as standard...
A final point: tune your engine to the max when the air is cool and moist (winter) and you'll have a very smoky engine in the summer (when there's less oxygen per litre of air, so you have set it up to over-fuel!!)
Simon Canfer

rossd · Unread post by **rossd** » 05 Mar 2004, 04:12

<blockquote id="quote">quote:<hr height="1" noshade id="quote">'m sorry but alot of you are wrong you can NOT run a diesel lean
by it's own design the air is a constant and fuel is varied to produce it's power so how do you run it lean?????<hr height="1" noshade id="quote"></blockquote id="quote">
Thats what Ive been trying to say, but not very well, look!

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Could you explain how they get hot? Diesels work by changing the amount of fuel injected to control engine speed. At tickover, just enough fuel is added to make the engine turn over at that speed,<hr height="1" noshade id="quote"></blockquote id="quote">
In fact thats awfully worded....

Kowalski · Unread post by **Kowalski** » 05 Mar 2004, 16:12

Increasing boost pressure increases cylinder temperatures and pressures, not because the mixture is being running lean but because air does not behave as an ideal gas and heats up when compressed, the more boost means more air more compression and more temperature.
Increasing fueling (assuming you don't overfuel) also increases temperature on a diesel, where as on a petrol engine this is not always the case (i.e. if you go from a lean mixture to a stoichiometric mixture the temperature can reduce).

Johnno · Unread post by **Johnno** » 05 Mar 2004, 16:37

I’ve been watching this thread with interest, and, apart from Kowalski above, I’m surprised that no one has mentioned the stoichiometric ratio. This is the ratio of air to fuel that theoretically results in complete combustion, i.e. no un-burnt fuel or air remaining. In a petrol engine this is about 14.7:1. Not sure about the diesel ratio (I can remember doing the vapour pressure & ignition tests at college but not the outcomes! Too many years ago) but the same principle applies to any fuel/air mix. The point is that there is a range of possible mixes, all of which will sustain ignition, at various efficiencies. It is also important to consider how combustion occurs. In a diesel, the fuel is injected over a period of time, either directly or into an antechamber, and upon entering the combustion chamber a pre-ignition phase occurs spontaneously at different spots (hotspots, if you like). As the injection stroke continues, the swirl created from the pre-ignition creates more complete mixing and combustion. This heats the charge and, presto!, the piston moves. At idle, and at light load, diesels run slightly lean. There is a rise in temperature over that which you would expect under ideal conditions, but it is within parameters. Press the loud pedal and more fuel creates greater overall heat energy (but not more efficient combustion) hence more power. When under load, forced induction from the increased velocity and mass of exhaust through the turbo means a greater mass of air into the combustion chamber, which will bring the fuel/air mix back towards the stoichiometric ratio. (I imagine that this will be one of the reasons why there is an initial output of smoke, which should then reduce as engine speed and airflow come back into balance).
I believe it is possible for a diesel engine to run too lean, and suffer damage. This is less likely under initial turbo boost conditions because, as mentioned by others, the excess fuel required to bring the turbo on-line will result in a rich mix. But this will be a temporary situation. As the air/fuel mix returns to a stable condition, and you return to a light throttle, you may have a lean mix producing sufficient power to maintain momentum but with a raised temperature. As an example, my BX DTR has an occasionally fit, where, under a sharp left hand turn, a slug of air that has gathered in the filter (a leak in the intake line, I think) passes into the injectors, effectively leaning the mix. This results in the engine speed rising sharply and power increasing, until the fuel delivery returns to normal. This occurs at low speeds and light throttle settings – i.e., no turbo. But I wouldn't want this situation to continue, as overheating will eventually occur.
This relationship between the fuel/air mix and temperature/power is one of the driving forces behind ceramic engines and high temperature components. Then you get into the area of combustion byproducts at elevated temperatures - let's not go there!

Unread post by **RichardW** » 05 Mar 2004, 17:32

>At idle, and at light load, diesels run slightly lean.
Er, no! At idle diesels run VERY lean - like 200:1!! There is no throttle on a diesel air intake and it only gets close to stoichiometic ratio at max wide open 'throttle' and full engine speed. It is this (partly!) reason that makes forced induction so easy on a diesel. There is a very good site somewhere that explains the relationship between boost pressure, injection duration, etc etc (I'll see if I can find it later on).

ActivaV6uk · Unread post by **ActivaV6uk** » 05 Mar 2004, 17:50

lol oh god what have I done!
the main thing that needs to come out of this is what will turning the boost up and not fuel do??? can any one actualy get some facts? other whise we have people who may be runing there engiens because they have read this thread...
Andy
Andy

jeremy · Unread post by **jeremy** » 05 Mar 2004, 21:32

Johnno
I think your 'speed-up' problem comes from a much less interesting source. If you have the roto-diesel pump the reason is that the governor (hence speed) control is accomplished using hydraulic ressure on the fuel instead of a mechanical linkage as in the bosch pump which uses rods. get air in the fuel - the mechanism fails and the engine can run-away.
There have been a number of posts on this site concerning this problem.
jeremy

Kowalski · Unread post by **Kowalski** » 05 Mar 2004, 21:50

From this discussion it is clear that some people just don't know how the diesel cycle works and assume that the diesel cycle is just like the petrol cycle when clearly it isn't.
Turning up the boost without adding fuel will probably make the engine less fuel efficient and will increase cylinder pressures and will increase N0x emissions. As for damaging the engine or even shortening it's life, it won't damage it, but will probably marginally shorten its life, but increasing the fueling to it's "correct" level would do even more of the above.

bernie · Unread post by **bernie** » 05 Mar 2004, 23:20

<blockquote id="quote">quote:<hr height="1" noshade id="quote">Originally posted by Kowalski

but increasing the fueling to it's "correct" level would do even more of the above.
<hr height="1" noshade id="quote"></blockquote id="quote">
Damage?