ive done some researching, and as an ex engineering major, and a current environmental science major (i know, oddest major for a rotor head, but i have common sense unlike most eco-crazies) i came across some interesting articles on the web. the first is new technology out where they have a computer mix a perfect mix of gas and diesel in a diesel engine to get 50% efficiency instead of 30% which normal diesels and most gasoline engines get.

http://www.gizmag.com/diesel-spark-plug-gasoline/12484/


Somewhere in one of the articles i read it said that it could be applied to both. it got me thinking. what if i were to add a small percentage of diesel into my gas tank. Would i get better mileage? would i get better power? i did some more searching and found another forum talking about it


http://ecomodder.com/forum/showthrea...ine-11163.html

turns out someone else has tried it and said it works. i'm going to go out on a limb and be the first to experiment with a rotary doing it. At first, i am going to do a basic control. i will see what my average mileage is for my current car. Then, i will start with 1/4 gallon of diesel which comes out to be way under 10% mix which the other guy used in the other forum. This will prevent me from doing something terribly wrong like all the knocking that will ensue from doing a harsh 50-50 mix. i may not see any marked difference, but what the diesel won't add in fuel economy/power, it could possibly add in lubricative properties due to it being a fuel/oil. We all know how important lubrication is for our precious engines lol.

feel free to add your comments/ideas as i only have one question. What will the diesel do to the seals inside the rotary? or i should say, what are the seals made of? i could do basic tests and let things of the same material soak in diesel prior to doing the experiment.

if this works, it could give both better fuel economy, and performance... theoretically.

 

i already hit a speed bump. did a search if diesel dissolves rubber. well, it does. i would have to replace all of my fuel lines to synthetic rubber. i think this bird crashed before it even took off lol. i could switch over all of my lines, but i don't have the money at the moment. though i think it would be more of a time issue than a money issue.

 

I experimented with cetane booster (combustion enhancer) in my daily driver, which is a low-compression piston engined car that would probably never ping. One person claimed to see a fuel economy increase from 13mpg to 18mpg. With the cost of the cetane booster at $9 per 16 gallons of gasoline, I figured that I would need to improve fuel economy from roughly 20mpg to 24mpg for it to cancel out its expense.

I did an A-B-B-A-A test. First the control MPG, then two tanks with the enhancer, then two more control tanks to ensure that the product was, if not completely out of the system, at least diluted down to negatable levels.

I noted, as did the person I learnt this from, that it required noticeably less throttle to drive down the highway, and exhaust was noticeably quieter. I could pull up certain hills at part throttle instead of full throttle. I was anticipating great gains.

Another thing that I noticed was that the engine felt "rough" at full throttle. It never detonated, but it wasn't too happy, either. Fortunately, I rarely needed full throttle anymore, so I continued on with the test.

What I found was that fuel economy did not change one bit. It stayed resolutely at 20mpg. I did the test twice, and got the same result.

I wonder if this other person's car had an EGR valve, which could have been opening more at the higher vacuum levels, thereby reducing pumping losses. My car does not have one, didn't need one since it has lower compression than most turbocars built since the 80s.

 

good experiment, with good methodology. never thought of using cetane booster. it could be different factors that played into the lack of change like different traffic conditions. but like you were saying with the EGR, it could also be different between cars. its the same thing with that tornado intake thing. some people get great effects while others do not.

im actually moving forward with the test despite it's setbacks. i would say a 10% mix wouldn't eat through my hoses that quick. i just got what my base gas mileage is approximately. my 83 doesn't have a low gas light so i'm gonna have to estimate. it also has a hole in the gas tank and will leak if its over 1/2 a tank. would use my 84 but its in awesome condition, and i would at least want to determine that putting diesel in a rotary isn't going to cause any detonation. i'm also running a slightly hotter plug than normal ( rx-8 leading plugs heat range 7) for my 84's leading plugs so im gonna have to do research on whether diesel is more prone to pre-ignition. on roughly 8 gallons i got approx. 120 miles which will give me around an abysmall 14mpg. think i may need to do another control cuz i did fix vacuum leaks and idle speeds during those 120 miles. my fan clutch is also seized which would also contribute.

i'm going to do an approximate 12% diesel mix (1 gal. diesel out of 8 total gallons of fuel) and let you know how the preliminaries go. if it goes well i'll move to my 84 which gets a constant 18.5 mpg's with a variation of half a gallon at the most, which i would accredit to traffic conditions.

i would say since diesel isn't as expensive as the cetane booster, then it wouldn't have to increase the gas mileage by that much to be cost effective.

 

heres an update. i filled it up yesterday making a half a tank total. i probably put half a gallon of diesel in there. drove it last night and it felt fine until i hit the higher rpm's. got to my friends house and it wouldn't hold an idle. wouldn't hold an idle all the way back home either. needless to say it was a "pray for no traffic lights" kinda night lol. just tuned it before. didn't mess with the idle speed, just the mixture. turned it about a half - three quarter turn rich, and it held a flawless idle. maybe not flawless, its still at around 1050 rpm's but it was a great imporvement from last night.

smokes a little bit extra on start up (guessing it's the diesel), but when its running, it burns clean. i feel a slight power increase. it is definitely noticeable that i have to push the pedal down less. i guess we'll have to see what the results come out to. since i put in a half a gallon, i'll put the other half in next fill up. hopefully i'll get a way better reading from this time cuz i would think that the lack of a good tune really messed up the experiment. will keep you posted.

 

another update. she's a little cold blooded and is hard to start up, but once she gets to temp shes fine. could possibly be that the plugs are old. definitely has a little more power, and definitely feels like i need less gas to take certain hills. i'm at about a quarter tank now and am at approx 70 miles. maybe a little more. that would put us at around 140 miles on 8 gallons, compared to the previous 120 miles on 8 gallons. 40 mile increase if you consider a full 16 gallon tank. that put my car from being a 14ish mpg car to an 18ish mpg car.

more testing is definitely to be done. if you were to ask my opinion on whether to do it, i would say it depends on your expertise with carburetors and the history of your car. my carb prob still has a vacuum leak somewhere which would make it even more difficult to tune for the diesel then it already is. having a good, working carb would also help. bad seals might also affect how the engine runs on the diesel mix. it might actually help a low comp engine run better. who knows? definitely will be doing a little more testing to see what the results are.

 

The car I tested with has oxygen sensor equipped fuel injection. One A-B-B-A-A test would take about one week. Almost entirely highway driving. You can see why I wouldn't mind saving a little bit on fuel.

As you point out, different situations like different things.

 

Diesel engines are not more efficient because of the properties of the fuel, they are more efficient because they have generally higher compression ratios and are unthrottled.

It is worth noting that diesel fuel has about 15% more energy per volume than gasoline, so there is some improvement possible from that if you can fully combust it. It is also worth noting that while modern ultra low sulfur diesel has more lubricity than gasoline, it is not a good lubricant at all. Older diesel fuels had decent lubricity, but that has changed with tighter emissions requirements. On a side note, AFAIK all the diesel rotary engines out there have still required oil injection to cool/lubricate the apex seals.

I certainly hope you see great gains, and I am glad you are taking the time to test the theory, but on a car that is apparently not in top mechanical shape anyway, and without any more accurate measurement than when the gas pump clicks, I will be very surprised if you see any gains greater than the error margin on your testing.