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Clooney Ive got an engine question I cant get off my mind.

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Chris

02-26-2003 15:49:26




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Clooney I know you have the answer thats why im asking. Why..... Is there not a gasoline "diesel"
I know this sounds dumb but i was thinking about it the other day i know high compression spark engines can preignite due to compression so theoretically why cant gas be injected through some kinda pump and be ignited at a certain time. I know there is a simple answer why ones not made but it sounds like a good idea. Thanks Chris

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Rick

02-27-2003 17:49:40




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 Re: Clooney Ive got an engine question I cant get off my mind. in reply to Chris, 02-26-2003 15:49:26  
Chris,
I'm a little late to the party but looks like you have some good responses. I would agree that lubrication would be an issue at the pressures required to overcome cylinder pressures.There are some systems that create pressure in the injector with a cam driven plunger. You would have to overcome plunger sticking issues as clearance would need to be very small. There have major advancments in injector controls in receint years. Timing and control of injection should not be a problem.

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guy

02-27-2003 08:40:56




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 Re: Clooney Ive got an engine question I cant get off my mind. in reply to Chris, 02-26-2003 15:49:26  
I believe the reason is the ignition characteristics of the fuel. Diesel has a low flashpoint so it ignites as soon as it hits the hot air. That allows the cylinder pressure rise to be controlled by the injection rate. The knock in a diesel ocurrs when some of the fuel does not ignite immediately and accumulates until it autoingites due to the temperature and pressure. Thats why diesels knock louder when cold, it is not hot enough to burn all the fuel as it is injected.

Gasoline is the opposite. It has a high flashpoint to it takes a higher temperature to light it. A spark is very hot so it lights it, but the air temperature in a diesel probably would not. Gas engines need to keep the mixture below the autoignition point until the spark initialized flame can burn it at a controlled rate. Knock ocurrs when some reaches the critical temperature near the end of the combustion and explodes.

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Bob K - clarification of flashpoint

02-27-2003 10:27:18




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 Re: Re: Clooney Ive got an engine question I cant get off my mind. in reply to guy, 02-27-2003 08:40:56  
I thought flashpoint was the temp at which the liquid cast off vapors. Diesel has a high flashpoint because it takes a higher temp to make vapors "flash off." Gasoline is just the opposite -- it gives off vapors at a very low temp, so it has a low flashpoint. Don't confuse ignition temperature with flashpoint temperature -- the two are typically inversely proportional.



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guy

02-28-2003 09:13:45




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 Re: Re: Re: Clooney Ive got an engine question I cant get off my mind. in reply to Bob K - clarification of flashpoint, 02-27-2003 10:27:18  
You are right, flashpoint is probably not the right term. My point is that diesel has to ignite quickly at the compressed air temperature, and it's ability to do so is measured by it's cetane number. Gasoline is the opposite, and it's ability not to ignite at high temperature and pressure until it gets the spark is it's octane number.



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G-MAN

02-27-2003 11:01:48




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 Re: Re: Re: Clooney Ive got an engine question I cant get off my mind. in reply to Bob K - clarification of flashpoint, 02-27-2003 10:27:18  
That's correct. What makes diesel ignite under compression is it's low octane rating. Octane is a fuel's ability to resist igniting under compression. Cetane is a fuels's ability to easily ignite under compression. I've seen guys say that octane is the same for gasoline that cetane is for diesel, and that's not true. They're actually opposite ends of the same scale, and are measured using the same equipment.
High octane = low cetane and vice versa.

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G Taylor.....already on the market for fishermen waterskiers

02-27-2003 08:30:57




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 Re: Clooney Ive got an engine question I cant get off my mind. in reply to Chris, 02-26-2003 15:49:26  
Two strokes with fourstroke torque,power,economy and emissions with the two strokes high HP to weight/size ratio are for sale now. Available at your Evenrude,Johnson and Mercury dealer. As for what is available in the automotive and industrial/ag market look at Popular Mechanics and Popular Science. They leak info months ahead of normal industry channels. maybe on purpose to test customer response?

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Clooney

02-27-2003 15:55:38




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 Re: Re: Clooney Ive got an engine question I cant get off my mind. in reply to G Taylor.....already on the market for fishermen waterskiers, 02-27-2003 08:30:57  
Glen, those DI outboards use spark ignition, they aren't compression ignition like a diesel. The fuel injection system is high pressure but doesn't use the injection for ignition it sprays the fuel in just after the piston closes the exhaust port so raw fuel isn't pushed out the open exhaust port. It's a good system but still injects well before the ignition sequence so the fuel can mix with the air for a combustible mixture.

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G Taylor

02-27-2003 17:05:52




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 Re: Re: Re: Clooney Ive got an engine question I cant get off my mind. in reply to Clooney, 02-27-2003 15:55:38  
I kind of figured it was at least a step in the direction of a gasoline engine injecting fuel directly into the combustion chamber instead of the port. Still have the throttle plate. At least an over all lean mixture can be used. Ignite a rich mixture near the combustion chamber center and let it burn until all the fuel is used and leave some surplus O2 left over. The "un-used" boundary area (at part throttle) against the walls would act as thermal insulation and prevent fuel condensation on metal surfaces. Low hydrocarbons and CO but NOX could be a bit high. Thank goodness for mass produced three way converters. It was be interesting to know what dark and mysterious fuel injection projects the auto makers are pursuing?

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Clooney

02-27-2003 19:01:42




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 Re: Re: Re: Re: Clooney Ive got an engine question I cant get off my mind. in reply to G Taylor, 02-27-2003 17:05:52  
Glen, there are a lot of trade offs as far as the auto makers are concerned with emissions & fuel economy being the big drivers of fuel injection direction. While one of the directions is direct injection it produces other problems, like serviceability of the injectors as they are usually buried deeply in the engine & are difficult to service. & high pressure fuel systems that are prone to problems overtime. They also carbon up easily if exposed & must be aimed exactly right to get the fuel spray near the spark plug. The big direction now is to get that darned throttle valve restriction out of the intake tract. That throttle valve is a big energy waster as it turns an engine into a big vacuum pump at low speeds & especially at idle. That uses energy that doesn't get returned to the drive train & is basically wasted. I think you will start seeing more powertrains without a throttle valve & just using valve lift & valve timing to control intake flow. It is a difficult thing to due at a production level as the cam controls to accomplish that kind of cam control is very complex. That is where the compression ignition engines really excel, you can idle a diesel for hours with very little fuel usage but try that with a comparable sized spark ignition engine with a tight fitting throttle plate & it will empty the fuel tank in much less time.
There is a lot of work being put into super lean combustion at low power demands & while it is possible to go to a very lean mixture if the fuel mist is placed at the EXACT spot required & at the correct time, one of the problems encountered there is the flame blowing out if anything is out of whack & that gives high unburned hydrocarbons. To get a super lean direct injection to work correctly it takes a well aimed intake port & well designed cylinder head to piston area to get the fuel spray to ignite & stay burning. That makes packaging the engine in an automobile difficult. Europe is taking a different approach on high mileage low emission engines & is leaning towards compression ignition diesel design, Japan is leaning more towards Hy-breds, & the US is covering all of the above, but is really leaning towards fuel cell technology.

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G Taylor

02-27-2003 19:35:14




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 Re: Re: Re: Re: Re: Clooney Ive got an engine question I cant get off my mind. in reply to Clooney, 02-27-2003 19:01:42  
A few more nuclear reactors can produce lots of hydrogen during off peak demand. Works good in a fuel cell and less CO2 emissions from breaking down natural gas. I see a small constant speed and load turbine in a hybrid before fuel cells take over. H2 has an octane rating less than ether and is nasty to store. Not practical for direct use in piston engines. Can also make clean buring,easy to store and transport methyl alcohol from nuclear steam, a catalyst and cheap abundant natural gas. Maybe a transition fuel? Or hydrogen blended with coal components for synthetic gasoline/diesel? In the short term a hybrid with a nearly constant speed,constant load spark ignition piston engine??? Easier to set up for emissions and economy by far. How did Deere rig up a variable speed drive able to stand farm use and abuse at that HP level and be efficient? Gives rise to an automotive application with a constant rpm spark or diesel engine running at peak torque rpm except when max HP is required. All we have to do is get people to pay for it.

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Dennis

02-26-2003 22:40:10




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 Re: Clooney Ive got an engine question I cant get off my mind. in reply to Chris, 02-26-2003 15:49:26  
Sirs, take a search of the BOURKE engine. Kinda sounds like a diesel running on gasoline. Interesting idea. Sorry for not remembering the website.



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HTR

02-26-2003 19:30:24




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 Re: Clooney Ive got an engine question I cant get off my mind. in reply to Chris, 02-26-2003 15:49:26  
Mitsubishi has a direct injection gasoline engine. This link is pretty good if you have patience to follow it.



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Will P

02-27-2003 17:43:08




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 Re: Re: Clooney Ive got an engine question I cant get off my mind. in reply to HTR, 02-26-2003 19:30:24  
That is a pretty kewl site. Thanks for sharing

Will P



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zane

02-26-2003 17:47:57




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 Re: Clooney Ive got an engine question I cant get off my mind. in reply to Chris, 02-26-2003 15:49:26  
One of the big advantages of direct fuel injection is that the duration of the combustion can be controlled by the injection system. Rather than take in a big gulp of air AND fuel on intake, the cylinder takes a big gulp of air only. Combustion then continues over most of the descent of the piston on the power stroke, as the fuel is injected, rather than suddenly after a spark plug, if present, fires. Thus preignition is minimal, since the whole dose of combustible fuel/air mixture is not available at ignition. Apart from the lubricating qualities and BTU value mentioned by Clooney, I'm guessing that fuel oil is more tolerant of the varying fuel/air ratio during the stroke, than is gasoline. Lean at the beginning, rich at the end. Or are the injectors sufficiently sophisticated to compensate? What about it, Clooney?

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Clooney

02-26-2003 18:58:45




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 Re: Re: Clooney Ive got an engine question I cant get off my mind. in reply to zane, 02-26-2003 17:47:57  
Zane, the electronics could handle the variable injector quantity but the injector response time couldn't keep up. There are some piezo injectors that might be able to do that though. There would be very little power derived form combustion near the bottom of the stroke anyhow. The secret of making a direct injection gasoline engine efficient is to inject the fuel at the last stage of compression into a small combustion area & get the fuel as close to the spark plug as possible, that allows a very lean mixture that will still ignite. On all that I'm familiar with the direct injection is not so much for more power but to allow a very lean combustion at idle & low power conditions & still get the fuel to ignite. The whole secret is getting as lean as possible a mixture to ignite & that takes getting the fuel as close to the spark plug as possible at time of injection.

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G-MAN

02-27-2003 07:39:10




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 Re: Re: Re: Clooney Ive got an engine question I cant get off my mind. in reply to Clooney, 02-26-2003 18:58:45  
The new High-Pressure Common-Rail injection used on the new Deere 8.1 Powertech engines (soon to be found on several others) can inject fuel for as long as you want it to, so maybe something like that will be the next step for gas burners. A dual-piston pump mounted externally on the engine provides up to 22,000 psi of injection pressure, and electronic injectors control the flow into the cylinders. They also run pilot-injection during warm-up, which allows a small amount of fuel to be injected before the main charge, to pre-warm the combustion chamber. It makes the engine much quieter at start-up, and then they really start hammering when they switch to full injection. It gets your attention.

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Chris

02-26-2003 17:32:23




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 Re: Clooney Ive got an engine question I cant get off my mind. in reply to Chris, 02-26-2003 15:49:26  
Clooney thank you for your quick and informative response as always. I had thought about the lubrication of the injection pump as a problem because i know they dont like gasoline. It was just a question that come into my mind and couldnt get it out. Thanks Chris



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Clooney

02-26-2003 16:52:25




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 Re: Clooney Ive got an engine question I cant get off my mind. in reply to Chris, 02-26-2003 15:49:26  
Chris, well sort of.... There isn't a gasoline compression ignition [diesel] that I know of. There probably is somewhere, but nothing being used that I know of anyhow. However there are high pressure direct injection gasoline engines that directly inject gasoline into the cylinders at compression. Those still use a spark to ignite the mixture but can hold the injection spray until the piston is at the correct position so it won't heat & preignite in a higher compression situation. Most automobile gasoline fuel injection systems inject the fuel into the low pressure intake valve area so a low pressure injection pump can be used. ~One of the big drawbacks of a compression ignition gasoline engine [or even any direct injection gasoline engine] is detonation, & that would destroy an engine is short order if allowed to continue.
~Even on the direct injection higher compression gasoline engines being worked with now most revert back to low pressure intake port injection for maximum power & high load conditions.
~Another draw back of a high pressure gasoline injection system is how to lubricate the high pressure injection pump & injectors [on a diesel the diesel fuel contains enough oil to lubricate the pump]. Most of the gasoline direct injection engines only directly inject at low engine loads so the fuel pump pressure is kept at around 50-70 psi.
~Using compression ignition on a gasoline engine would be chore as the injection would have to be timed perfectly & the intake air would have to be directed into the cylinders perfectly to keep it from igniting as it first starts coming out of the hot injector. The other thing would be that gasoline has less BTU's per gallon so why not just use diesel oil with more power per gallon. Gasoline would also need a lower compression ratio so some efficiency would be lost there. ~One of the big advantages of a compression ignition gasoline engine would be no throttle plate to block the intake to raise manifold negative pressure [vacuum] & that would increase the engine efficiency due to lower pumping losses.
~Along the same lines there are some other things in the direct injection area that are being looked at but I really can't comment on those without getting clearance first.....

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