biodiesel as fuel additive for gasoline

[The Toecutter]

Hell, I really wouldn't 'need' more than 20 horsepower in a 1500 pound vehicle with good aero, but there's that aspect of performance that I'm also aiming for. I want something that nothing on the road would be able to keep up with.

[Lug_Nut]

Originally Posted by omgwtfbyobbq

IDIs make peak torque at really high speed for a diesel. The TDIs make it lower, and each one has it's pros/cons... Just make sure you don't go over 7k rpm, I've read the valves can float.

The closest comparisons I can make is the VW AAZ and 1Z diesel engines. Both have the same 79.5 mm bore and 95.5 mm stroke (1.9 liter displacement). Both are turbocharged, came with catalytic converters and EGR systems. The big differences are the AAZ has pre-chamber heads, the 1Z is direct injected. The AAZ has a nominal 22.5:1 compression ratio, the 1Z has a 19.5:1 ratio.
The AAZ makes a peak of 55 Kw (75 hp) at 4200 rpm and has a flat torque output of 150 Nm (110 lb*ft) from 2400 to 3400 rpm.
The 1Z makes a peak of 66 Kw (90 hp) at 4000 rpm and a peak torque output of 202 Nm (149 lb*ft) at 1900 rpm.
If the claim is that the IDI peak occurs at a higher rpm than the DI, then yes, that is true. However, the peak is significantly lower.
The 1Z TDI makes 75 hp or more from 2250 to 4400 rpm. The 1Z makes 110 lb*ft of torque or more from 1200 to 4200 rpm.

Seven thousand rpm from a diesel? Not from looking at my dyno charts. I can't get over 5000 rpm. I believe the piston is being pulled down by the con rod faster than the flame front can push.

[omgwtfbyobbq]

Originally Posted by Lug_Nut

If the claim is that the IDI peak occurs at a higher rpm than the DI, then yes, that is true.

Originally Posted by omgwtfbyobbq

IDIs make peak torque at really high speed for a diesel. The TDIs make it lower...

Yup, pretty much.

You need to get around the fuel cut to make power past ~4500 rpm with an IDI. Although, as the post states, going past ~5500 is kinda pointless because of the limited amount of air the head can flow. Supposedly, any diesel is ultimately limited by the fuel/air mixing rates.

Direct injected engines like the TDI are similarly mixing-rate limited, hence the lower redline than IDI Diesels. If high RPMs are a priority, then the IDI is preferred. They have a stock redline exceeding 5000 RPM.

Probably because the prechamber affords some sort of cushion for combustion, but that's just a guess. This is also probably why the torque curve is so flat. The passageway between the prechamber and the cylinder limits the flow of energy, unlike in a TDI, where the combustion process can transfer all the energy in a much smaller time frame. Power wise, an IDI should make more per liter than a TDI, but isn't as efficient due to more area in the head for heat to soak out of. Advances in electronics led to pilot injection to quiet the engines down, which finally allowed higher efficiency DIs in passenger cars. Intercooled VNTs also helped out in the efficiency ballpark...

[GasSavers_nathan]

so i filled up today, 26.93MPG. last two tanks were 22.6 mpg and 21.48.
nearly 5mpg higher then the last two tanks, in case you're wondering i was getting around 21mpg same time last year.

changes were:
one liter biodiesel.
i drove about 60km highway where i normally don't have any.
outside temps are starting to rise.

i usually struggle to get 27 even in summer. my highway FE isn't great either, last trip was around 30 and it was in summer iirc.
so anyway, I'm not saying biodiesel was good for 5mpg but it may have helped.
I'll run this tank without any mods and see where it ends up.

[GasSavers_Ryland]

did you add that liter of biodiesel to the numbers when you figured out your mileage to make sure your numbers were counting it as fuel used?

[GasSavers_nathan]

sure did, that would have effected my last tank anyway, not this one.

[GasSavers_nathan]

So now that I'm back to normal gas I've noticed a couple differences. One is the car seems to have more power, this could be(quite likely) caused by the warmer temps outside now. The second thing I've noticed is the exhaust smell, its stronger then with the bio. At times reminding me of a chainsaw exhaust, kinda burns the eyes a little. My cars not in a great shape of tune though.
Misses and stalls quite frequently at idle. Maybe a weak ignition system? or maybe I need a set of better spark plugs.

[GasSavers_nathan]

Gassed up again, no bioD this time and i got 26.73, last tank with the bioD it was 26.93 under similar conditions.
So it appears to make no difference, although i would like to revisit this later, maybe with some way of better tracking FE. and try different ratios.

[zpiloto]

So you had 2 tanks with bio-diesel around 27 mpg and one tank without at the same? Why not run another tank without and see what it does before you give up on it. Did you check the plugs?

[ELF]

Originally Posted by nathan

Misses and stalls quite frequently at idle. Maybe a weak ignition system? or maybe I need a set of better spark plugs.

If your car is not in good running condition your not going to get any kind of consistent results when adding different things in to your gas.
Your first consideration should be tuning your engine.