Raising TDI compression

Re: Raising TDI compression (A2RicedGTI)

Raise the compression ratio???
IDI pistons are flat on the crown. They will absolutely NOT work with the TDI.
Also, raising the compression ratio beyond a certain point causes a WORSE surface to volume ratio, worsening heat transfer losses. I would say that at 19.5:1 compression of the stock TDI, it's already near that limit where increasing the compression ratio will not significantly increase the temperature at the end of compression.
I hate to discourage you, but I think E85 will not work adequately on a true compression ignition mode without a Diesel pilot ignition or at the very least, glow-plug assist. The Methanol fueled research engine that I mentioned before based on the TDI with 20:1 compression is spark-ignited to give you an idea oh how difficult it is to autoignite alcohol fuel. Ethanol autoignites 973 degrees Fahrenheit; adding gasoline to the blend will reduce it only marginally. By comparison, Diesel fuel autoignites at about 600 F or 33% less. This means your end-of-compression temperatures, at the most simplistic level, need to be FAR higher than 973 F.
Your team has some VERY ambitious ideas for a powerplant for which I applaud you, but might I suggest again that you address the fundamentals rather than trying to reinvent the wheel with the realistic resources you have?

Re: Raising TDI compression (A2RicedGTI)

Is all this business about the temperature not being high enough just at startup, or the entire operating range? Have any idea what temperature TDIs run at during various RPM loads? We will probably run between 2000 and 3000 rpm (three static settings- very low load, low load, and high load). Depends on how the thing runs on a engine dyno (we have to track one down...all we have right now is a chassis dyno...Im sure there is one somewhere on the central coast).
Have any idea at what temperature the engine block or pistons will melt? Probably want to stay away from that...
Ok I just learned that just running glow plugs wont fully burn the fuel mixture and will create lots of soot. But I also learned that large trucks run 23:1 on E95, but they use 2 stroke engines...There are companies out there that convert large diesel trucks to run E85 or E95- they raise the compression from 18 or so to 24 or 25 and probably do some other stuff. (not exactly sure...boardering on trade secrets there...of course, we also have "top secret" Ford documents). Also working on figuring out the exacty differences on the new greet cars vs their non-green counterparts (ever see an S10 (or whatever) with a little green tree on it somewhere? Those can run ethanol 85 out of the pump and normal (aka low octane- so they cant raise the compression ratio too much) gasoline. Of course, they arent really reaping the full benefits of Ethanol, which is why we are avoiding them...)



[Modified by A2RicedGTI, 7:06 PM 2-7-2002]

Re: Raising TDI compression (A2RicedGTI)

Wouldn't advancing the diesel injection pump timing (up to just below the danger point) accomplish roughly the same objective: increased cylinder pressure
It's easy enough to blow a piston by going too far with the pump timing, let alone going to higher compression.
If I were you, I'd do some more research on injection pump timing adjustment (advance it) and see if that might be an easier, less costly option.
On the subject of octane, yes higher octane fuels are more resistant to pre-ignition.
But if you are looking to get the highest thermal efficiency out of your project, stick with high cetane diesel. In order of energy content per lb of fuel => Diesel / Gasoline / Ethanol
Are you looking to make the engine less efficient?
Or is this a "senior design project" where "E85 is the only fuel available?"

Re: Raising TDI compression (A2RicedGTI)

Hi.. I drive an older Turbo Diesel, and I believe that the compression ratio is 24:1 on it. Turbo is pushing 20-24 PSI boost. It is not a TDI, but is the older direct injection type, with a mechanical injection pump. It will run on almost anything once up to temperature. I have seen kits availiable to run it on used fryer grease. http://www.greasel.com/.
Not sure if it would run on ethenol though. Injection pump might not like that. If you need parts, or help on an older VW diesel.. This guy knows what he is doing and has both new and used parts. He is located in Ohio. http://vwdieselparts.com/ This engine is very simple and very reliable. It does not make the HP that the newer TDI's makes but, It might suit your needs. Good luck on your project.

Re: Raising TDI compression (84QuantumTD)

The compression ratio on the on the 1.5 IDI was 23:5:1; 1.6 IDI was 23.0:1 and the 1.9 IDI was 22.5:1. Your `84 would have been a 1.6 with 68hp stock.
Yikes, with the boost upped to that kind of levels, I'm worried that you may blow a head gasket. Do you have the fuelling turned up?
A2, I'm still working on getting to all your questions, but I was busy all weekend and away from my office until today.
I will say though that advancing the injection timing further will not help startability significantly, but instead lead to serious engine damage Plus, even if you can get it to work, past a certain degree of timing advance you'd lose engine efficiency and performance.


Dave


[Modified by tdimeister, 4:04 PM 2-12-2002]

Re: Raising TDI compression (tdimeister)

Hi.. I was posting that info for A2RicedGTI.. We were talking about alternative fuels, for his project and I mentioned that the older diesels were fairly forgiving about different fuels. They will run an almost anything as long as it has a flashpoint similar to diesel, and isn't chemically damaging to the injection pump. My owners manual even says you can use up to 50% kerosene or 15% unleaded gas in the winter to keep the diesel from geling.
I got the compression info from my owners manual and turbo info from a web site. Here is the link. It is VERY detailed....and VERY VERYCOOL. Even has emission info. http://4crawler.cruiserpages.com/Diesel/SAE/vwtdsae.shtml
I looks like scanned docs from the original manufacturing. It has info on the 1.6L 4cyl, and the 1.9L 5 cyl turbo diesels. It shows the pressure info in Bar so it's possible I messed up the conversion. It shows a range of 1.6 - 1.6?? bar @ 3000 RPM, and 1.6?? to 1.7 bar at 4500 RPM (which is redline). A Garrett Air Research turbo was used on the 4cyl and a KUHNLE KOPP and KAUSCH turbo on the 5cyl. It has the waste gate info and all the engine specs. I would recomend checking this site out... It is really cool. If you like engines, and engineering type stuff. have fun !!!!

Re: Raising TDI compression (tdimeister)

Hi... Sorry my mistake... I assumed the max pressure was the boost, must have missed the wastegate opening info. Nice to know they engineered a large margin of error though. I wonder if I could get more boost out of it .... Probably not a good idea concidering the mileage on it. It sure is a nice running engine. I have driven a TDI.. WOW. It's like a gas engine as far a quiet and smoothness. But I kinda like that clattery DIESEL sound mine makes .. The Cummins in the Dodge trucks sound even better. As far as the TDI is concerned I have seen on the VW web sites that they make A LOT more engine variants in the UK. one is 150HP and 236 lbs.Ft. Why don't we get those engines? Could you chip/modify a TDI to make that much power? The torque would be unreal. Anyway...I guess I will just have to be happy with my 68HP... By the way I don't believe that stat.. I mean my car is no rocket for sure, but the car is very capable of getting out of it's own way. Feels way more than 68HP even my un mechanically inclined friends look at me funny when I tell them it's 68Hp. Mabye the torque is deceiving me but it's only like 90 Lbs.Ft .I can even spin the tires in first, and chirp second if I shift really hard. I don't usually do this as I drive about 600 miles a week and I like my clutch/trans. Anyway enought yakkin.. Thanks for the info. Have a great day. Diesel On