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tdirs1 (Automotive) (OP)
31 Jul 05 17:45
Does anyone know what ideal fuel air ratio of a diesel is ?I know a petrol engine is 14.7 to 1.
ivymike (Mechanical)
31 Jul 05 18:14
It depends on what you mean by ideal.  Stoichiometric AFR for diesel fuel is about the same as that for gasoline.  "Ideal" AFR depends on what your goals are - but often AFR for a diesel is set in the neighborhood of 28-32 under "typical" part load conditions.
Retracnic (Automotive)
31 Jul 05 18:41
I don't get your question. The vast majority of diesel engines are not throttled, so a stoichiometric fuel mixture is never achieved during normal operation. Thus making the ideal AFR a moot point.

Good Luck
Bryan Carter
ivymike (Mechanical)
31 Jul 05 21:57
ret - are you saying that you can't control AFR in a diesel?  I'd be inclined to disagree with that statement...
franzh (Automotive)
31 Jul 05 22:26
Here we go again Ivymike!
If you try and throttle a diesel engine, you will indeed chop power, but diesel fuel has a very wide air-fuel flammability limit, somewhere around 3 to 42:1.  With diesel engines, the fuel can be ignited and additional air force fed for additional power, (add on turbo kits, bigger flowing turbos, exhaust systems).  You can also have a fixed amount of air and increase fuel (power chips, which change the fuel delivery curve, or larger flow injectors, or modified pumps) which will give additional power, but with tons of smoke.
I played around with a diesel throttle once in an attempt to reduce NOx, but was not happy with the results.  If I decreased the airflow without decreasing a proportionate amount of fuel, I had a weak engine with copious amounts of smoke.  To my knowledge, there are no throttled diesel engines anywhere.

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ivymike (Mechanical)
31 Jul 05 23:32
Here we go again Ivymike!
Sorry, I don't have any idea what you're talking about...  Do you disagree with what I've said above?  

I've seen at least one throttled diesel, but it wasn't a production application.  The things that come to my mind for influencing AFR in a more-typical diesel are:
Amount of fuel injected
Amount of boost allowed (assuming electronic wastegate control)
Fraction of EGR used

I've seen some smoky high-perf applications with AFR below 20:1.  
ivymike (Mechanical)
31 Jul 05 23:59
I think I've figured out what your "again" comment was in reference to - still burning up about the compression ratio discussion from 6 months ago?  I'd forgotten all about that.  I was right, though (still am).  nah nah na nah nah.

tdirs1 (Automotive) (OP)
1 Aug 05 3:15
The lastest VW 16v 2.0 tdi engines have a motorised throttle body and lambda sensors to part control egr and fuel ratio.The reason for my question is to work out engine power after cylinder head flow before and after porting.I will be racing and using on the roads 1 of these engines in a mk 2 Golf,which i raced before with the 8 v tdi engine in.
franzh (Automotive)
1 Aug 05 8:35
Me burned up?  Here in Central Texas?  Never!  But I do thoroughly enjoy a lively discourse!
I seem to remember an SAE toptec discussion about 10 years ago about the use of a throttle on a diesel engine, to control NOx.  This is the time when EGR's were just getting into the research arena.  Now, since almost all of the major OEM diesel engine manufacturers use EGR and not throttles, even though EGR has a few drawbacks, it apparently was the more effective technology.


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SMOKEY44211 (Automotive)
1 Aug 05 12:13
I've read about and conducted some experiments relating to homogenous charge compression ignition diesel fueled engines. It would appear under these conditions an air fuel ratio in the neighborhood of 14.7:1 would be at or close to the ideal mixture. Getting the engine internals to live with that fuel load is another matter. As would be expected tha Nox #s go down as you increase the fuel load. The diesel converted model airplane engines seem to survive ok but the wrist pin seems to be the weak link in larger displacement trials.------Phil
patprimmer (Publican)
1 Aug 05 18:57
I am pretty sure some small Japanese diesels had throttles back in the 70s. I am not sure why as it would effectively reduce cylinder pressures and could suppress ignition if taken to far.

As far as I know, power is controlled in a diesel by fuel metering, not air metering, up to the point where there is more fuel than the unthrottled airflow can use, ie excessive black smoke.


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Helpful Member!(3)  crysta1c1ear (Automotive)
1 Aug 05 21:41
The original question mentions 14.7 so it's pretty sure the intention was to find out the stoichiometric air fuel ratio.

CxHy + a(O2+0.79/0.21N2) => xCO2 + y/2H2O + a*0.79/0.21N2
where a=x+y/4 since a C can use up a whole O2 and an H can only use 1/4 of an O2. The 0.79 and 0.21 are the proportions of N2 and O2 in air.

If you take the formula for a hydrocarbon reacting with air you can easily work out how much of each is required.

molecular weight of O2 is 32 and N2 is 28.
Octane C8H18 has a=12.5 and molecular weight 114 ( 8 12's are 96 plus another 18).
Dodecane C12H26 has a=18.5 and molecular weight 170.

So if you crunch the numbers to get the AFR
AFR = a(MWO2+0.79/0.21*MWN2)/MWfuel
you get 15.06 for petrol and 14.95 diesel.

Since hydrocarbons are mainly H-C-H, two to one, and the odd hydrogens at the ends making the difference are light, all the hydrocarbons will have similar stoichiometric air fuel ratios, with the exception of the very light ones where the two extra hydrogen makes up a significant proportion of the weight. Take CH4, the H-C-H weighs 14 and the two H's weigh 2. That's a large portion compared to 2 in 114 or 2 in 170.

So AFR for methane calculates to 17.2 and Ethane to 16.1.
Then propane 15.6 and Butane 15.4. You can see the figures closing in on the figure 15 for petrol and diesel.

Now if you add oxygen things change drastically since oxygen in the fuel means you need less oxygen from the air. And since air is 4/5 nitrogen, if you can cut down on a certain amount of oxygen then you reduce the amount of air you need by a factor of about 5, (drop 4 N2s for each O2 dropped). So the AFR for a fuel like ethanol works out to be about 9.

Now if you say that US gasoline is like petrol but cut with about 5% ethanol you can calculate 5%*9 + 95%*15 = 0.45 + 14.25 = 14.7 and get anAFR for gasoline.

So providing the diesel is all hydrocarbon based the AFR will be around 15. Diesel of plant origin (biodiesel) has oxygen in it and the AFR will be lower and mixtures would be in between, in the same way that the AFR for gasoline is between that for petrol and ethanol, heavily weighted towards the petrol figure. I don't think the figures change much if you take air as being 78% Nitrogen and 1% Argon instead of 79% Nitrogen and as I said before, changing one heavy hydrocarbon for another won't make much difference, ie calculating diesel as a coctail of hydrocarbons would only complicate the calculations and not significantly change the result.

ivymike (Mechanical)
1 Aug 05 22:11
I'm sure that stoichiometry calculations are all good fun for engineering students, but wouldn't it be a whole lot simpler just to pick up an introductory book about IC engines (Taylor or Heywood or Pulkrabek) and look in the appendices for a table of the same?  Perhaps we should have just suggested that initially.

Interesting "rule of thumb" about stoich AFR approaching 15:1 as the caterpillars get longer.  

(I'm glad to see that your interpretation of the question and your calcs both agree with my initial response, though)

tdirs1 (Automotive) (OP)
2 Aug 05 19:00
Thanks all for your in put basically the ratio is almost the same a petrol motor from what i can gather,not what expected!!
franzh (Automotive)
5 Aug 05 8:36
One thing I remember from "way back" while attending a class, is a diesel engine takes in air and allows just enough fuel to "get the job done".  At idle, that is indeed just a smidgen of fuel, for a barely usable amount of power.  The AF ratio there was very high, somewhere around 40:1 if I recall.  On a non boosted engine, just add more fuel and power and rpm's increase.
Try and toss in 14.7:1 air to diesel at idle and you have a very, very fast idle!


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Helpful Member!  SomptingGuy (Automotive)
5 Aug 05 9:51
Diesel engines produce their maximum torque rich of stoichiometric, even though it gets smokey and inefficient that side of the line.  To limit the amount of fuel available to each injection, rotary pump (e.g. the Lucas DP range) manufacturers fitted (I think the term was) scroll plates.  These limited the travel of the pumping plungers so that the fuel accumulated could never exceed stoichiomentric requirements.  Scroll plates were adjustable so that the same pump design could fit different engines.

In the days before turbocharging was the norm, the only way to get more torque out of your diesel engine was to open the bonnet and tamper with the scroll plates.  If you loosened them off and turned them a bit you could turn your taxi from a slow clean vehicle to a fast dirty one.

Methinks many black cabs had "adjusted" scroll plates in those days.
ivymike (Mechanical)
5 Aug 05 11:44
Full bore, I am sorry to say, I think was 1 part in 25,000. Long time ago, I may be wrong  
Sounds like you're talking about volume of fuel:volume of air.  The rest of us are talking about mass of fuel:mass of air.  

A Diesel has not quite enough energy to keep running at idle from the heat of compression. Just a smidge of fuel keeps it ticking over.
Out of curiousity, are you at all familiar with the first and second laws of thermodynamics?  What would they say about an engine running at idle from the heat of compression?

ivymike (Mechanical)
5 Aug 05 14:06
(or in the case of AFR, mass of air:mass of fuel)
frankiee (Marine/Ocean)
5 Aug 05 19:26

With a diesel fuel oil consisting of 86.5% C, 13.2% H, 0.3% S and 0%O
14.55 Kg air to Kg fuel
kenre (Mechanical)
6 Aug 05 8:22

 you are indeed correct on throttled diesels, have seen them myself. they had a throttle in the intake manifold like an injected petrol engine. The big dfference was it controlled vacuum available to the injector pump for injection control.
Throttle pedal wasnt connected directly to injector pump.
My guess is it was a crude way of limiting the amount of fuel injected at lower engine speeds to reduce the exhaust smoke.


crysta1c1ear (Automotive)
6 Aug 05 17:06


     ____    _                        __           ___      ______  ____
    / __ \  (_) ___    _____  ___    / /          /   |    / ____/ / __ \
   / / / / / / / _ \  / ___/ / _ \  / /          / /| |   / /_    / /_/ /
  / /_/ / / / /  __/ (__  ) /  __/ / /          / ___ |  / __/   / _, _/
 /_____/ /_/  \___/ /____/  \___/ /_/          /_/  |_| /_/     /_/ |_|
                    __ __       ___  __ __        ______  ______
                 __/ // /_     <  / / // /       / ____/ / ____/
                /_  _  __/     / / / // /_      /___ \  /___ \
               /_  _  __/     / / /__  __/ _   ____/ / ____/ /
                /_//_/       /_/    /_/   (_) /_____/ /_____/
Thanks Frankiee.

Let's take a look at your figures.

With a diesel fuel oil consisting of 86.5% C, 13.2% H, 0.3% S and 0%O

86.5/12=7.21 where 12 is the molecular weight of carbon.

So ignoring the 0.3% sulphur, we can pretend your hydrocarbon is C7.21H13.2. (I'm not saying the molecules are that short, I'm just thinking about the carbon hydrogen ratio.)

CxHy + a(O2+0.79/0.21N2) => xCO2 + y/2H2O + a*0.79/0.21N2
where a=x+y/4

in this case, a= 7.21 + 13.2/4 = 10.51

AFR = a(MWO2+0.79/0.21*MWN2)/MWfuel
AFR = 10.51 (32 + 28*0.79/0.21) / (86.5+13.2)
    = 10.51 * 137.33 / 99.7
    = 14.42

14.55 Kg air to Kg fuel
So a rough calculation for your fuel (ignoring the sulpher in the fuel, argon in the air, etc) gives 14.42 which is pretty close to the figure you gave - not that I ever doubted you, ..., more a question of trying to understand why things are the way they are.

So why the difference to the earlier estimate?

If hydrogens were about 2:1 with the carbons, we could expect an AFR a bit below 15 as indicated earlier.

7.21*2= 14.42.
The actual percentage hydrogen you give is 13.2, ie less that 2 hydrogens per carbon.

The picture above is a naphthalene molecule. Similar molecules in diesel allow the ratio of hydrogen to carbon to be lowered to less than 2 to 1. The article where I'm leaching the above picture from
gives typical quantities of naphthalene related molecules in diesel. The quantites are significant. Bearing that in mind I think your figure of around 14.5 is better than my estimate of 15, for the reasons stated.


franzh (great posts on gas engines by the way franzh, thanks) mentioned that diesel engines (by which I really mean compression ignition) could run on just a smidgen of fuel. I thought about that.

Since the fuel is ignited by the temperature of the surrounding compressed air I assume that there is no limit to how lean the mixture can go - two molecules remote from each other will both ignite. It's just that going too lean would mean that friction would cause the engine to stop. On the other hand I assume that a spark ignited engine requires a sufficient concentration for a flame to propagate.
tbuelna (Aerospace)
7 Aug 05 6:21
Direct-injected, compression-ignited engines always combust at near stoichiometric, if the engine is designed properly.  The fuel injected will only combust when sufficient oxygen is present at the flame front. The fuel will continue to burn as long conditions are suitable within the combustion region (ie. oxygen, fuel and heat).  If the available oxygen within the chamber is used up before the available fuel, soot is created.  If the heat in the combustion zone is reduced sufficiently, due to expansion of the end gas and slow combustion, combustion halts and the remaining fuel and oxygen are dumped out the exhaust.  If more oxygen is pumped into the woking chamber than is necessary for the amount of fuel injected, then engine efficiency is reduced.

The basic nature of a compression-ignited means that it can run "lean" or "rich" without doing damage to the engine.  Ultimately, the amount of fuel delivered is dictated by the load on the engine, and not by the amount of air flowing past the throttle as in an SI engine.
Helpful Member!  Dzltec (Automotive)
8 Aug 05 7:16
When we dyno vehicles to fault find, we also check boost pressure and air fuel ratio with a wide band lamba senor at the exhaust pipe.

The ideal ratio is 18:1 for good power and very minimal smoke emmisions.

This has also been proven after we reconditioned the pump and injectors for this vehicle. Too low a/f and they get smokey, too high they can lack power. At  a cruise situation they can go as high as 40:1.

You can go lower with a/f but the exhaust temps start to rise pretty quickly on  a turbo application.

Hope this helps.
SomptingGuy (Automotive)
8 Aug 05 7:24
Does anyone know how low you have to go with a/f to kick off a DPF regeneration?
turbomotor (Mechanical)
9 Aug 05 11:57
Hello tdirs1:

Your string generated a lot of discussion.  We engineers are an opinionated lot, aren't we?

I'll add to the fray:  Ivymike suggested some IC engine texts that may be helpful.  My personal favorite is a book by Obert of U of Wisconsin - Madison.  Obert's book includes a chapter on fuels for SI and CI engines that includes many neat hydrocarbons and the combustion data associated with those neat hydrocarbons.  I find the tables to be very practical and useful when considering potential alternate fuels.

Also, it may be hard to find, but Pratt & Whitney used to publish an aeronautical handbook that had gas properties for products of combustion (100%, 200%, and 400% theoretical air) of a CnH2n hydrocarbon with air.  I have found this data to be very useful, especially when evaluating the available energy in the exhaust products of a turbo diesel motor.

tdirs1 (Automotive) (OP)
10 Aug 05 3:20
Wow some good info fellas thanks,especially about oxygen levels in exhaust.Ive been toying with the idea of installing a lambda sensor to keep track of oxygen levels but ive not had a base reading to go for.Ill tell you all the base of what im doing,im building a Golf a2 with a 16v 2.0 tdi engine in from an a5 Golf,it should run Bosch edc 16 management but ive decided to run the earlier Bosch edc 15 which doesnt require a motorised throttle body for egr.I ve ported and flowed the cylinder head had some injector nozzles flowed,installed a 4 branch stainless exhaust manifold and a Holset HX35 hybrid turbo.I will be using it primarilt on the road so good emission will be essential and occasionally be heading for the drag strip.The power i am aiming for is between 310 to 330 hp.
tdirs1 (Automotive) (OP)
15 Aug 05 3:17
I will be using a lambda sensor and reader to keep track of emissions.There are some pictures of my turbo install on tdi club website on the news from the batcave thread.
Rob45 (Automotive)
17 Aug 05 10:42
My guess is you can't go low enough on A/F to kickoff regeneration of the diesel particulate filter since going low drops the exhaust temperature.
That's why Cat is using the fuel-added afterburner.
ivymike (Mechanical)
17 Aug 05 13:19
Somtinguy, you should start another thread.  I'll do it for you, in fact.  thread71-131992

Rob45 (Automotive)
15 Sep 05 13:29
You made a comment 'way up-thread that isn't what you'd call entirely true:
" Now, since almost all of the major OEM diesel engine manufacturers use EGR..."

In fact,  I only know of Cummins employing EGR; Detroit may, also,  but the two of them together don't produce nearly as many diesel engines as does Caterpillar,  who do NOT use EGR.
franzh (Automotive)
15 Sep 05 21:42
No challenge from me on raw numbers even if I would have to think about it for a bit, but most of the worlds advanced diesel engine builders have acknowledged that the use of EGR, Urea injection, aftertreatment, particulate traps, will be necessary for 2007+.  Cats use of their advanced engine management system has been successful, but my inside sources say it was a real challenge to get and keep it there.  Cat makes a great product and their market share is well deserved, but this is no place for semantics.  

The diesel industry has its work cut out for itself for the next two iterations of emission certification.  I read Diesel Progress monthly, and my related trade journals, plus sit in on our engine development meetings, and the topic of diesel emission attainment is a top and hot topic.  Almost everyone agrees that EGR is the most successful means of meeting '07, even with its problems.  I feel we havent seen the full breadth of the research needed for the next 10 years.

Let the hounds loose, the advanced diesel technology will persevere.

This is certainly a new topic area, Rob45, why don’t you kick it off?


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UWH (Mechanical)
16 Sep 05 0:35

As far as I know pretty much all the major diesel manufactures except Cat use EGR to meet Tier III EPA emissions.

Cat took a bold step in developing their ACERT technology instead of going the EGR route.  And they paid something like $7K per on-highway truck engine in penalties a couple of years ago because they weren't ready with the technology.

I believe the major hurdle with EGR going forward is the size of the air-to-air aftercooler needed to cool it and overheating in souther climes.
SomptingGuy (Automotive)
16 Sep 05 9:22
I was under the impression (from the industry rags) that EGR and SCR (with urea) were competing technologies and that there was a broad split between Europe/USA as to which to use.  The problems with each approach being that EGR compromises efficiency; SCR requires some method of policing the urea addition.
franzh (Automotive)
16 Sep 05 10:10
EGR is used pre-combustion, urea is used post combustion.  There is no reason they cannot be used together.  Your second comment about policing the urea is certainly valid.

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turbocohen (Automotive)
28 Sep 05 21:01
Urea is a huge nono upstream, too corrosive.
tdirs1 (Automotive) (OP)
19 Mar 06 4:51
Seems to me Audi got the ratio pretty much spot on judging by the lack of smoke and noise on the R10 at Sebring.
waross (Electrical)
19 Mar 06 8:29
I'm puzzeled by the comments that the stoichiometric mixture is not or cannot be controlled on a diesel engine. I was under the impression that that was the purpose of the aneroid valves used with early turbo chargers. Didn't the aneroid valve hold the mixture to near stociometric at full trottle until the boost pressure built up?
Helpful Member!  GregLocock (Automotive)
19 Mar 06 18:18


Greg Locock

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ivymike (Mechanical)
19 Mar 06 21:28
the a/f ratio IS controlled, just not to the stoichiometric a/f ratio!
tdirs1 (Automotive) (OP)
20 Mar 06 2:49
Whats an aneroid valve?
ivymike (Mechanical)
20 Mar 06 8:51
I believe it was to restrict fuel delivery until boost reached desired levels, to keep the A/F ratio appropriately lean (and avoid smoke).
waross (Electrical)
20 Mar 06 9:07
An aneroid valve is a device that measures the manifold pressure. It controls the fuel delivery. It prevents the fuel control system from delivering more fuel than there is air to burn completely. They were used on truck engines to prevent the plume of black smoke that occurs with full throttle application at low RPMs, before the turbo boost builds up.
GregLocock's post is probably correct in that the early aneroids often didn't work as planned and over-restricted the fuel at low RPM so much that in a tough spot, a truck engine often could not develop enough torque to get the truck moving. Construction sites, logging, gravel pits, starting on steep grades etc.
Many aneroids had to be removed and given a "flotation test" before the truck could do its job.
(Flotation test,- Throw it in the river and see if it floats!)
drwebb (Automotive)
20 Mar 06 9:21
gives typical quantities of naphthalene related molecules in diesel"

Be aware that "napthenics" are saturated hydrocarbons (i.e. not aromatic) very different from naphthalene- a particular 2-ring aromatic compound that smells like mothballs.  It is unfortunately confusing nomenclature, but while diesel fuel is made up of almost half naphthenes, there is little if any napthalene in it.

Likewise, the common solvent called "naptha" has no naphthalene in it.
GregLocock (Automotive)
20 Mar 06 18:33
waross, diesels do not work anywhere near stoich for most of their operating range.


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patprimmer (Publican)
20 Mar 06 20:29
I would have guessed that at full throttle, slightly richer than stoic would give maximum power irrespective of pollution, and about stoic or just leaner would give maximum power without excess smoke.

Like I say, just a guess, and obviously much leaner than stoic at part throttle.

I use the word throttle figuratively for the speed and power control device or the pedal on the right hand side of the floor.


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waross (Electrical)
20 Mar 06 22:25
Hi greg


waross, diesels do not work anywhere near stoich for most of their operating range.
I knew that, actually.I appologise if I wasn't clear in my previous post.
I was under the impression that the aneroid valve knew that also. However, in the pre-computer engines, the fuel charge at low boost would theoretically go rich of stochiometric when the pedal went to the metal. At this point I understood that the aneroid valve would act to hold the mixture at stociometric or less to avoid the smoke plume.


Didn't the aneroid valve hold the mixture to near stociometric at full throttle until the boost pressure built up?
To answer my own question, it was supposed to, but it didn't work very well and it often over compensated. In my area, in those days, most of the drivers and/or owners of turbo-charged work trucks gave the aneroid valve the flotation test. (Dump trucks, logging trucks, any trucks liable to face unusual conditions requiring full torque to get moving.)
Am I misusing any technical terms here. I thought that I understood what stochiometric meant.
GregLocock (Automotive)
20 Mar 06 23:19
Stoichometric is the perfect air fuel ratio, ie two oxygen atoms per carbon, one oxygen atom per two hydrogens.

Now, I think it is a bit of a furphy (red herring) in the case of a diesel, as they are effectively stratified charge engines, so the fuel does not come in contact with all the air. Nonetheless by the normal SI definition (mass air/mass fuel) a diesel is operating  lean, even when it is belching black smoke. If it were truly operating at stoke then it would produce the same torque per unit swept volume as a gasoline engine, for the same VE (crudely), NA.

For instance, this 4 litre gasoline engine I happen to have under my desk, will max out at 383 Nm of torque, whereas an equal displacement non turbo four stroke diesel will struggle to reach 200 ft lb, or 260 Nm, according to this:


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tdirs1 (Automotive) (OP)
21 Mar 06 2:55
Suddenly Greg i just got it!!so the reason it is a red herring is due to the fact the diesel is injected into compressed and heated air into the cylinder and not into the airstream as a petrol.
Helpful Member!  CCycle (Automotive)
21 Mar 06 16:04
CI engines usually top out at 0.6 to 0.7 of stoichometric.  
That is the number given by Heywood.
Any more fuel results in smoke.
The problem is to get the fuel in contact with the O2 and as mentioned above, the burn front will be in zones where the ratio is near stoichometric.
For this reason Direct Injected CI engines will never reach the specific power of a SI engine at a given input pressure.
The DI CI engine always runs lean which has serious consequences for catalysis.  
Reducing cats do not work hence the problem in cleaning up NOs.
GregLocock (Automotive)
21 Mar 06 20:48
260/383= 0.68

funny that!


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globi5 (Mechanical)
27 Mar 06 14:24
Just to clarify:
Reducing cats do work in cleaning up NOx but require urea.
(They sell it as AdBlue:
SD22 (Automotive)
9 May 06 12:45
Franz (et al):  I know this is an OLD post but I found it via a Google search.

Air throttled diesels ARE around. I drive one ... a Nissan SD22 naturally aspirated four cylinder. It has a Bosch inline injection pump with a PNEUMATIC governor (and a centrifugal governor). The throttle pedal is cabled to an air throttle body.  This provides a vacuum signal to the pneumatic diaphragm on the injection pump ... which in turn positions the fuel rack depending on the vacuum vs. spring signal.

Rob45 (Automotive)
9 May 06 13:41
UWH wrote:
"I believe the major hurdle with EGR going forward is the size of the air-to-air aftercooler needed to cool it and overheating in souther climes."

Another big hurdle may well turn out to be the corrosive products of combustion that condense out in your shiny new aluminum intercooler...
JackFu (Automotive)
9 May 06 13:42
A Hyndai diesel tubocharged engine is also equiped with a throttle. if there is no throttle, when the intake air is boosted, the pressure at the EGR outlet may be higher than the pressure at EGR inlet, so EGR function is invalid. I think that a throttle is used before the EGR outlet can control the pressure, as to ensure the EGR function working.

kenre (Mechanical)
10 May 06 9:33

Thats the engine i seen it on!!  but this engine was fitted into a Holden Panelvan.....   No idea why!
 Any ideas why they used that system?  must have something to do with reducing black smoke from overrich mixtures.

blondesgetit (Automotive)
24 May 06 22:59
Pump systems use a throttle. Fuel injectors are self throttling. I'm probably going to over-simplify but in Henry Ford's world that was the way to progress.
In electronic fuel injection, fuel is injected thru a narrow port that determines PSI. This is where the mathematics begins and it ends at the injector tip. Everything between is a created environment, subject to assigned parameters and machining variation. Black smoke is indicative of poor surface finish. It allows fuel to pocket. This alters the oxygen mix when it releases and is not likely to coincide with combustion. Black smoke is the result of unspent fuel releasing due to vibration. Regarding the use of test fluids - Do any of you drive a vehicle? Go park it anywhere for 3 months and look at the parts. Water of any kind is unacceptable; alcohol can be corrosive. Viscor is the correct fluid BUT it needs to be circulated.
Within the injector, conductuity and tempurature is held relavent to incoming fuel and air. The goal is to keep the fuel mist airborne and at a sustained pressure while any over delivery is rapidly burned to a carbon which is systematically directed to a dump port that recycles any unspent waste. Composition weight assists the process.
SD22 (Automotive)
7 Jun 06 12:45
Ken:  The Nissan SD22,23,25 naturally aspirated often have the air throttle/pneumatic governor Bosch inline pump. But depending on delivery location, these same engines may also be fitted with the more familiar Bosch VE rotary pump which does not require an air throttle because the VE has a mechanical throttle governor.

The RBD-MZ inline pump uses an air throttle for NOX emissions. Remember, these little diesels have 23:1 compression, indirect injection, and base injection timing of 20 degrees. Combined, these three factors contribute significantly to NOx emissions. So ... reduce compression at low engine loads by throttling intake air (reduces compression). Were you to retard base injection timing significantly, exhaust soot increases (not desireable).

In the USA for emissions reasons, the SD22 was fitted with the air throttle/pneumatic governor pump and EGR.

oxilume (Civil/Environmental)
29 Jun 06 23:49

Your answer is simple.  It is the LEL and UEL of a diesel and air mixture;

LEL = .6%
UEL= 7.5%


If you are going to conduct any R&D with flammables you better know the LEL and UEL with respect to the oxidizer.  70 or 90% Hydrogen Peroxide is much different then air.  Likewise, if using O2 don't forget that air is only 21% O2.

When running hydrocarbons through a high temperature plasma system thoroughly having control of the oxidizer and fuel is critical if you don't want to launch the plasma torch and yourself into sub-orbit.


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