RE: post turbo
haha
thanks for the flames
If you're interested, I've replaced 2 racing turbos from excessive runtimes at 1200 degrees with my friend's race car, logging dozens hours over it's life. Yep "logging". I'll go dig up the charts if anyone wants to see 1200 degrees for a solid hour pop a probe right off, when the datalogger carefully and diligently records the death of the engine over a few short seconds.
Can a diesel like one on a deuce run 1200 for over an hour? Sure it can.
Can the probe fail in less time? Yep.
Would it be smart to just probe the rear of the turbo and tune for full load at 1100 degrees. I'd say so - you'll have a lifetime of good engine left to use.
So let me expand on that a bit before I go to bed:
More boost does not = more power, more airflow does, however.
--Get a bigger turbo and get rid of the one that just runs high psi and high egt. Having a small turbo is like an asthmatic breathing through a straw; lots of effort, not a bit of power developed.
Low EGT is not safe without knowing your a/f
--Even diesels have them, but they are a tad more tricky, running sometimes 100:1 at idle, 23-30 part load, and stoic only under full load
Oh - what's stoic on a diesel?
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 1
.
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 c0cktail of hydrocarbons would only complicate the calculations and not significantly change the result.
Ok, that's egt, probes breaking from stress, and how afr fits in - all in one post. Hope that helps someone!!!!
