CrackHeadMel

iTrader: (2)

Shoot this down if i missed something obvious, or its already been proven wrong, however my google search reveled nothing.

Why not use diesel as an aux injection under highboost engines? it burns cooler and slower than convential gasoline, and its available at the pump?

Just pondering

SaabGuy

Actually pound for pound gasolene has less BTU

Also engine compression is too low my jetta has over 500 psi compression per cyl and a healthy rotary has like 115. It will never burn

Sent w/ blackberry

CrackHeadMel

iTrader: (2)

what about a turbo rotary, not a n/a one? say 300ish psi.

and if ive missled, i dont mean to replace gasoline as the fuel souce, the idea was to use diesel as an aux injection

SaabGuy

Youd have to have a supper fuel delivery system for the diesel fuel. My car (jetta) injects the diesel at about 20,000 psi and uses glow plugs not spark plugs.

SaabGuy

Not to mention Diesel engines run on like 100% preignition which is certain death for turbo rotary engines

rotarygod

iTrader: (1)

Diesels do not run on preignition or detonation. That is a huge misconception. They have perfectly controlled flame fronts. They just do it differently. Proper fuel management is critical. Direct injection makes this possible. Diesel fuel actually has a very low octane level which is a resistance to knock and nothing else. It is somewhere between 20 and 40. When you inject fuel into the airstream and compress it with the air, it gets much hotter and hits a detonation threshold earlier. I know there are people that will cry foul with this and say that running too rich can cool a charge down but understand that we are talking within an optimum range here. When you run too rich or too lean from optimum, heat goes up in both cases. Then after a certain point on each end of the lean/rich spectrum, it goes back down again.

If you were literally just to inject diesel through an auxiliary injector, you would detonate. Remember that detonation and rate of burn don't necessarily correspond. Alcohol may be a slower burning fuel than gasoline and have a higher octane rating but diesel fuel doesn't. It merely burns slower. It's octane rating is higher. Since diesel fuels are rated in Cetane, it's hard to ever find any octane information on them but it's low.

By controlling the spray of diesel fuel into the combustion chamber at the right time and with careful control of the spray pattern, they can ignite it controllably as it sprays. The only thing that makes this possible is the rate of burn and not it's octane level. Modern diesels use very high injection pressures upwards of 20,000 psi or higher. You can't do this with gasoline though as the flash point of gasoline is much lower. Moder direct injection gasoline engines are up near the 2000 psi mark. The higher the pressure and the better the ecu controlling the spray along with well designed spray patterns, the more precisely we can control fuel delivery and burn rate which is why modern engines keep getting away with higher and higher compression ratios.

There are people working on gasoline engines that run with no throttle plate solely through high pressure injection much as modern common rail diesels do but their big problem is flame front control. It's not a detonation problem. It's that gasoline burns too fast and is much harder to control. When you lose control of the flame front, you detonate. This is not what diesels do. It is controlled. An engine designed for manifold injected gasoline will not work well with diesel. However a diesel rotary can be made to work. It's been done but don't think it's a simple conversion for a street car.

Sorry for the rambling.

CrackHeadMel

iTrader: (2)

Thanks for the clarification. I was under the impression that the fact that diesel took a much higher compression ratio to ignight that it had a higher octane rating

I knew how diesel's injected fuel, however you putting it out in reference to my thread makes why it wont work make sense. Diesels arent compressing the air and fuel together, where in my case i would be

thanks

-Jacob

slo

iTrader: (1)

I disagree with this part of your statment. The main problem is exhaust heat. Cat converters in the exhaust need to see at least 800F to light and stay burning. Running ultra lean mixtures results in very cold exhaust temps and emissions issues.

There was an article detailing the mitsubishi GDI system which stated exactly that.

Durring extended high speed operation they can even fully open the throttle plate of a throttle by wire system and controll engine speed and output soley with fuel.

There is another article detailing these issues specific to the rotary engine

"A study of a direct-injection stratified-charge rotary engine for motor vehicle application".

Its too large to post but I could send you a copy if your interested.

rotarygod

iTrader: (1)

I have that SAE paper on the rotary. My friend Jeff is actually hosting all of the SAE papers that a few of us have accumulated so far. Feel free to download them.

http://www.mazdamaniac.com/direct_dl.htm

Low exhaust temperature is a problem (only to the EPA!) with a throttleless system but only from an emissions standpoint. You can use a throttleless system on a direct injected engine but there are a few different apporaches to DI that you should look into. The approach that you are referring to still used a spark plug to ignite the fuel. What I am referring to is compression ignited gasoline. This has been done with limited success so far and the holdup is with the fast burn rate of gasoline making it difficult to control the flame front. Sorry if I didn't make that more clear. I probably could have.

rotarygod

iTrader: (1)

Diesels did inject fuel conventionally in the intake manifold in the past. Catepillar engines from the 70's and probably much later were a prime example of this. They also ran very low compression ratios of about 7:1. They had to so they wouldn't detonate. They ran roots superchargers to make up for the compression ratio and were limited to much lower rpm limits than todays diesels.

slo

iTrader: (1)

Thanks for the link, and that makes allot more sense.

It would seem like a compression ignition dirrect injection gas engine would primarily be a matter of precice control over the injection events, many modern diesels inject fuel slightly after TDC to lower nox emmissions at the expense of reduced fuel economy.

Also when you say the flashpoint of gas prevents pressure from going over 2000 psi, how does it become a vapor at that high of a pressure, and how does it flash without oxygen present?

rotarygod

iTrader: (1)

It's not that gasoline can't go over 2000 psi. It should be able to just fine. The real question is can it go up to 20,000+ psi? I've often thought about how there would be a problem with it going this high since there is no oxygen present and I can't think of a reason. It's just merely a concern. The biggest issue with taking gasoline up real high is primarily based on lubrication capabilities of the fuel. Diesel fuel is a lubricant. The high pressure pumps they use are also lubricated by the fuel flowing through them. This would not work with gasoline as it doesn't lubricate. It would be very hard to design a pump that would go this high that uses a separate lubrication system due to sealing issues under such high pressures. I have no doubt that as people find new ways of building fuel pumps, we'll see pressures go higher and higher. I see the day when the line between a gasoline engine and a diesel engine starts getting pretty thin in terms of fuel efficiency, power, and emissions. It's not to say they'll ever be equals but we are already seeing them have more in common with each other than engines of the past.

Diesel rpm limits are going up. Diesels have used direct injection for a while now. It's the newest thing in gasoline engines. Diesels have been throttleless for a long time. Modern DI engines are approaching this and have done so in lab tests. Gasoline engine compression ratios are going up and paradoxically diesel engine compression ratios are going down. Diesel engines are getting quieter so their "rattle" isn't as obvious. Diesels are getting cleaner in emissions and so are gasoline engines. Fuel injection pressures are rising in both. Both are getting variable valve timing and even variable geometry turbos are appearing on both. The difference between each engine type is getting less and less with each new engine generation.

patman

iTrader: (3)

^ yes, but it still remains that diesel is easier to make and has a higher specific energy content. and for the most part, diesels can do now what people are still trying to do in preliminary research for gasoline engines. Our country may be retarded as far as fuel choice, but if you look at the rest of the world, especially europe, it is obvious that diesel is the fuel of choice....

of course if you want to really optimize, everyone should be driving electric cars and recharging them from a grid fueled by combined cycle solid oxide fuel cell/regenerative gas turbine power plants, with a little extra on the side from renewable sources... we all gotta dream.

food for thought...in europe they are building gas turbine plants with >60% efficiency. a combined fuel cell/turbine could do around 70. in this country the average power plant efficiency is in the nighborhood of 23%. some technological powerhouse we are....

theres my rant for the day

pat

SaabGuy

FYI my jetta got 45mpg last week with 50/50 city highway.

patman

iTrader: (3)

my rx7 got 8mpg!

ericgrau

iTrader: (1)

Typical power plant efficiency is 40%, which I believe is good for a practical power plant. That number may have increased since I heard it.

Europe likes diesel because it's more economical. Diesel engines are heavy, which makes them impractical for performance. In Europe they have engines that are much smaller than anything sold here. Even the gasoline engines are available smaller. At $6/gallon they care more about economy. Yeah, I know Audi won Le Mans with a turbo diesel but 1) It's heavily turbo'ed and 2) Those races are 100% rigged. They put on restrictor plates to balance all the cars, supposedly to make it a close race. Audi also wins by being able to swap out entire sections of the car in seconds. So they can destroy the entire rear end, for example, and just swap it out.

Research has not yet been successful with HCCI (homogeneous charge compression ignition). That's premixing fuel and air, then igniting it with compression. Diesels compress then inject fuel, whereas gasoline engines premix the fuel/air and then ignite with a spark. Both premixing and compression ignition typically means detonation. I think Honda has an HCCI engine prototype but it only works under constant throttle. And I think it runs on gasoline not diesel, for some reason.

patman

iTrader: (3)

That number is a little low for modern plants, but not much. My point is that 60% can be attained and that we are using old plants that are super inefficient.

Modern diesel engines are only slightly heavier than gasoline engines. A turbodiesel with a similar torque curve will be 30% more efficient, and maybe 10% heavier than it's gas counterpart. Sounds like a damn good trade to me.

Pretty much all HCCI engines run on gasoline, diesel works fine the way it is, there really isnt much need to change it. The point of an HCCI engine is to remove the throttle from a gas engine, because there are huge losses around the throttle valve. The problem is that it is pretty much impossible to control transient combustion event timing, there are way too many variables.

rotarygod

iTrader: (1)

I'm not sure where you get your info but it needs a serious update. HCCI is running on gasoline (ethanol, butanol, etc) and not diesel. If it ran on diesel, it would be a diesel. HCCI is applying compression ignition to fuels other than diesel.

Detonation comes from a lack of flame front control. The whole point of direct injection and HCCI is to better control flame front propagation so that we can be more efficient by moving the detonation threshold up.

Here is a link to a working driving HCCI that GM is working on. This is recent news. Their engine doesn't control HCCI at all speeds and rpm's yet so it has a transition point to conventional spark ignition. It is still a working running engine though which means that experiments have in fact been successful. It is no longer theory.

http://www.autoblog.com/2007/08/24/g...ng-prototypes/

patman

iTrader: (3)

i wonder how much of their control strategy is based on real time data and how much is a transfer function which could potentially change as the engine ages and loses compression or builds carbon...?

want some more interesting reading material that has nothing to do with the OP's topic?
check this out:
http://www.unh.edu/p2/biodiesel/article_alge.html

ReZ311

iTrader: (4)

Diesels DO DETONATE! That's how they function. The intake stroke, compression of the air to 500psi heats the combustion chamber up, then direct injection of diesel fuel (NOT JET FUEL!) at top dead center, then the detonation of the diesel fuel, which is the power stroke. The glow plugs do not function once the engine warms up. There is nothing different about it. It's controlled detonation.

Diesel fuel will never work on a rotary because the flame front is too slow.

CrackHeadMel

iTrader: (2)

So a diesel runs with uncontrolled flame propagation? With cylinder pressures spiking massively from combustion cycle to cycle? because thats what your saying

rotarygod

iTrader: (1)

No diesels do NOT run on detonation. I'm not sure where your info comes from but it's flat wrong. You may own a diesel but you still need to do some homework on how diesels work. Please don't talk to some idiot diesel mechanic. MOST mechanics out there are complete idiots when it comes to how things work. Just because they've fixed random parts on a vehicle for 20+ years doesn't mean they know a thing about how or why it works the way it does.

Detonation has nothing to do with a diesel and it is equally as bad on a diesel as it is a gasoline engine. Detonation is a lack of control of flame front in which multiple flame fronts form and randomly collide. Diesels have a controlled flame front through design but mostly due to the slow burning nature of diesel fuel. They have one flame front and that means there isn't detonation. Just because you have compression ignition does not mean you have detonation. It is a misconception that they run on detonation. They don't. No engine does. At least not for long.

Diesel can work on a rotary. It's a 4 stroke engine. That's all that's relevant. Even a 2 stroke can be made into a diesel. Flame front is slow with diesel fuel. That's why diesels don't rev as high and also why flamefront is easy to control. It makes no difference if it's in a rotary or not. The biggest challenge with the rotary is the fact that we not only compress air, we also move air. If you make the rotor dishes smaller to raise the compression ratio, you also make it harder to move air through the dish and around the engine. We don't leave it in one place like in a piston engine. You are really limited to about 11:1 compression ratio as a result although power doesn't really change appreciable between 9:1 and 11:1. It falls off quickly above and below these points. This means we can't make a really high compression ratio which is optimal for diesel. To fix this we must do one of 2 things. One is that we have a spark ignited diesel. The lower compression really offsets any potential power from the higher energy content diesel fuel. We do ned to add some boost to give it a higher effective compression ratio. Don't only focus on static compression ratio. The other option is that we have a full time glow plug.

A company called PATS has a wankel apu (auxiliary power unit) for business jets that is a diesel. It is not common rail or direct injection but is the older semi direct diesel injection with a glow plug. It most certainly does work though. Higher fuel pressures as in modern common rail systems may make things a bit easier. Someone just needs to spend the time and money to make it work.

slpin

iTrader: (9)

uhhh diesel do NOT run on detonation
if you own a diesel and think it runs on detonation, maybe you might as well start putting gasoline in it...