|Oct 31, 2012, 09:38 PM|
spark ignition diesel...
and why not? i have heard refferences to *(very) old 2 cycle spark ignition diesels. one guy on youtube got pretty good atomization from SVO (straight vegitable oil) buy running it at 200 bar (1 bar = 14.7 psi, so 280 psi) though a jetta TDI injector.
diesel is about 7 times thicker than gasoline. stociometric AFR is 14.6 :1 vs gasolines 14.7 to 1.
biodiesel (meth ester something or other) is pretty close to diesel, and when properly made has a ph of 7. seems to have very little real world problems with rubber seals, tho the current E90 at the pump has caused failures as well.
BTU of biodiesel seem to be higher than gasoline.
so why not use a fuel injected, biodiesel in a spark ignition engine?
|Nov 21, 2012, 08:58 AM|
1) Because you don't need to.
2) Petrol will "Gassify" under pressure, and sprayed in. Bio-Diesel will turn back into a liquid in the intake track.
3) If you spray it into a combustion chamber that has low enough compression, so the fuel doesn't auto-ignite (to control timing with a spark) you won't have enough pressure and heat to properly burn the fuel. (you will make a lot of soot) To get my Cummins to run clean... the engine starts at 22:1 compression, and then runs 32 psi boost. That would bring the static compression up to 6x a typical gas engine. (at about 800 to 1000 psi compression, under boost)
So... I'm all for experimenting... but what would the reason be, behind this experiment? If you want to make bio-diesel... burn it in an engine that is designed to burn some kind of "Oil." You got to remember... the original diesel engines were designed to burn peanut oil, and not this petroleum crap that the oil companies want us to use. Diesel was the original "Green" fuel, and we can make Bio-Diesel out of dam near anything. (Pressing any vegetable mater, old coffee grinds, algae, grass, or used oils) Heck... I pour old engine oil, and transmission fluid directly into the tank of my 2001 Dodge Cummins. (runs fine)
Basically... making bio-diesel can come from 100's of waste sources. To make bio-Petrol (alcohol) it has to come from prime food sources (Corn, sugar cane, sugar beats) and that's BAD for the economy. (and just stupid since the power out is nowhere near the power in)
|Nov 21, 2012, 12:29 PM|
what is 'gassify'?
i did not know you could turn a liquid into a gas, i always thought you just made smaller drops.
the reason i was wanting to was to avoid paying 4 a gallon and to see if it could be done.
i figured if you get the droplet size small enough, you would have complete combustion and avoid soot. a cummins diesel is totaly differnt than a spark ignition engine, so im not sure if the two apply.
ususly what is good for th economy is bad for my bank account
|Nov 22, 2012, 07:56 AM|
Don't get me wrong... If you think that you can get it to work... then go for it, and let us know what happens. Also... I totally agree. $4/gal sux. But, get a car/engine that is designed to burn it.
I've been tuning engines for a long time (see the screen name)... and I've played with dang near every fuel that can be used. Along with that... I own a custom bike shop, and I like diesel. (Oh... and I have a degree in experimental Physics)
I can help with any info you may want, to help you with your experiment.
The problem with using oil for a fuel (Any form of diesel) is that it burns slow, and is hard to ignite. So... way back when... rudolf diesel decided to make an engine that would simply raise the temps, internal of the engine to the oil's auto-ignite temp. In doing that... he also was compressing the fuel to a point that would accelerate the burn.
Above, you say "A Cummins is different than a spark ignition engine." And you are absolutely right. As I already said... the main difference is in the cyl pressures before ignition. With the relatively low cyl pressure of a typical spark ignition engine.. you won't be able to extract enough energy out of the fuel before the end of the "Power" cycle. You make mention of "Complete combustion"... but an engine turning 3000 RPM only has a fraction of a second to make that combustion happen. (With out exploding the fuel)
With that said... how do plan on getting complete combustion inside an engine with low cyl pressure, and volumetrically designed to spin as high 6000 RPM? (FYI... my Cummins has a redline of 3200 rpm, and makes peak torque at 1900)
As a final FYI... Back in the late 70's, early 80's... Chevy tried to do a similar experiment. They basically took their 350 gas engine, and put high compression heads on it... with dished pistons... and tried to sell it as a diesel. It was a piss-poor engine, and it didn't live long. Also, it was HIGHLY inefficient. Most of the world is split 50/50 gas/diesel... but in the USA... we are mostly gas in the consumer market. And that's mostly becasue of the F-ups that the "Big 4" did in the 70's... and that kept the market from growing. And... to this day... they keep saying... "The American Market doesn't want diesel !!!" Personally... that's a bunch of bull !!! If the car companies would bring in some good diesels, and give the same incentives as gas... people would buy them. (The MPG alone would sell them) Since you are looking at Diesel... here's some things to think about.
1) VW's "Sign and drive event" that is currently going on... EXCLUDES the TDi cars.
2) Toyota has been selling diesel versions since the 60's. They won't bring them into the USA because of our "dirty fuel." Well, we now burn ULSD, and they still won't bring them into the country.
3) Ford, Dodge, and Chevy all had a 1/2 ton diesel truck ready to come out... and then they never were released because "of the bad economy." Cummins designed a brand new V8 5ltr engine for the Ram 1500, and the project was scrapped.
4) The only government subsidies for Bio-Diesel is to produce fuel from Soy. Soy beans have almost NO oil in them, and the extraction process uses caustic chemicals. You can get more oil out of old (used) coffee grounds. (and that's reusing waste, not a farm product)
As I said before... I like diesel.
|Nov 22, 2012, 08:21 AM|
And... as an FYI to this... a modern "Common Rail" diesel engine will run pressures around 1600 BAR in the rail. Yep... that's 23,000 PSI.
As I recall... the pressure in my VP Cummins is around 29,000 PSI. AND... I've hear of some systems going as high as 45,000 psi.
|Jan 15, 2013, 12:49 AM|
in doing some more reading, ive found some refferences to old tractors that started on gasoline, then used the engine heat to 'thin' diesel and burn it.
but at this point you need to redesign the fuel system and pretty sure you need a computer controling it.
edit: some quick rearch show diesel fuel at 190F has a viscosity of 1.1
gasoline is .88 (i asume at 60f or 20C)
water is 1.0 (at 20F)
so if you can preheat the fuel to 190F (my car runs at 195 and has coolant lines to the carb), then this is not so far fetched.
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