DIY_EFI Digest Friday, April 30 1999 Volume 04 : Number 251 In this issue: Re: Direct Injection Re: cam grinds for SC Re: Fuel injection plugs Re: Fuel injection plugs Re: Fuel injection plugs Re: Fuel injection plugs Re: Fuel injection plugs Re: Fuel injection plugs Re: Fuel injection plugs Re: Fuel injection plugs Re: Fuel injection plugs Re: Direct Injection Re: Need Fuel Injector Data Re: Fuel injection plugs See the end of the digest for information on subscribing to the DIY_EFI or DIY_EFI-Digest mailing lists. ---------------------------------------------------------------------- Date: Thu, 29 Apr 1999 21:09:45 -0400 From: "Gary Derian" Subject: Re: Direct Injection With port injection, the best atomization is letting the fuel puddle on the back of the valve then hitting it with a blast of exhaust when the intake valve opens. On SEFI when does the fuel inject? Isn't it when the intake valve is closed? Maybe someone here has actual data. Remember, the cylinder pressure exceeds the intake pressure when the intake valve opens. Gary Derian > > > I am aware of Orbital's work. Their system is a great way to make a 2 > > stroke meet emission requirements. The air assisted injection is necessary > > to achieve fuel air mixing in a limited time since injection occurs after > > the exhaust port is closed. > > You mean intake port? It is necessary to obtain acheive the mixing in the short > period of time, a plus is the good atomization. > ------------------------------ Date: Thu, 29 Apr 1999 21:14:54 -0400 From: "Gary Derian" Subject: Re: cam grinds for SC To my mind, roots type or centrifugal type superchargers would both benefit from small overlap cams. This is because these are the only engines that have greater intake pressure than exhaust pressure. Too much overlap just blows intake out the exhaust. Gary Derian > > I'm about to install a Vortech supercharger on my SBC 305 TPI, and > I'm thinking about changing cams too. The vortech FAQ has > this to say about cams: > > 4) What is the correct cam to run with my > supercharger? > > Cam selections are best discussed with the various > cam manufacturers. Many people select cams which > are not the correct choice for centrifugal > superchargers. When discussing the cam with a > manufacturer make sure they understand a Turbo cam > or a cam for a Roots style supercharger is different > than a centrifugal cam. Generally speaking the > supercharger and the cam do the same thing (increase > volumetric efficiency), be cautious of choosing a cam > that has large amounts of lift and duration. Ideally for > a street application retaining decent idle, emissions > and drivability are important, for this reason we > suggest a "moderate" camshaft. Given the choice > between two cams we suggest the milder of the two for > street applications. > > Of course that is of little help, and I would like some idea of what's > going on before contacting manufactures. So, what does make for a good > cam for applications like this? How do these cams differ from turbo or > roots specific cams? > > john ------------------------------ Date: Sat, 1 May 1999 19:14:10 -0700 From: "Howard Wilkinson" Subject: Re: Fuel injection plugs Greg: I must point out that this statement is erroneous: > Gasoline also has more energy per unit >>volume than diesel fuel, right? > >They are really quite close on a volume basis! within 2% or so, with >gasoline a bit ahead. Actually on a weight basis they are quite close..... by volumn diesel has considerably more energy. There is actually a fairly close correlation between fuel energy and fuel weight. H.W. - -----Original Message----- From: Greg Hermann To: diy_efi@xxx.edu Date: Wednesday, April 28, 1999 10:26 PM Subject: Re: Fuel injection plugs >>Greg Hermann wrote: >> >>> An Otto cycle is actually MUCH more efficient at full throttle than a >>> diesel, especially if you only consider the "air efficiency"--adding fuel >>> to the mix brings it closer to a diesel, but not down that faR! >> >> It is my understanding that a 4 stroke gasoline engine is roughly 25% >>efficient, where a diesel is roughly 35% effecient. > >The difference MIGHT be almost this big at part throttle--but the >difference is due mostly to pumping losses, not necessarily to >thermodynamic superiority > > It is also my >>understanding that effeciency is defined as the (amount of energy >>produced)/(amount of energy used). > >This is correct. > > Gasoline also has more energy per unit >>volume than diesel fuel, right? > >They are really quite close on a volume basis! within 2% or so, with >gasoline a bit ahead. > >So given the same volume of fuel used and >>roughly equal power output, the gasoline engine will be less efficient. I >>know, I know, they don't have the same power output. A diesel engine does use >>more fuel than a gas engine because of it doesn't mix well right? > >No--more like it cannot burn all of the oxygen it breathes in, so it cannot >make as much power. > > It seems to >>me that the increased pressure of a diesel further tips the scale in diesels >>favor though. > >See below about which engine has higher peak pressures. > > For a given volume of fuel, a diesel produces roughly twice the >>pressure as a gas engine right? > >Not at all--only place the pressure is higher is at the top of the >compression stroke, prior to ignition/injection. > > Feel free to tell me where I goofed, I'm just an >>engineering student learning.... > >Where you goofed is by just applying pv=nrt. > >The power that you can (ideally) get out of a given amount of gas will >always be limited by the (useful) delta T times the specific heat times the >mass flow. The "useful" delta T is limited by the available expansion >ratio. If the gas is losing heat to the water jacket as it expands, you >will get less than the ideal amount of work out of it. > >T1/T2= (P1/P2) exp (0.283) = (V2/V1) exp (0.4) ----These exponents are for >air, and would change somewhat for different gasses. But plenty close >enough to figure out how things work. Likewise--specifc heat varies with >both pressure and temperature, but holding it constant is close enough to >get a GOOD feel for how things work. > >The ideal work out of a power stroke, W = (T1-T2) x (specific heat) x (mass >flow). > >As you can see from the first equation, (V2/V1) ---the expansion ratio-- >determines how much delta T is possible with a given engine design. >But--since we are talking about RATIOS, a higher absolute T1 allows more >work from a given mass flow at any given expansion ratio. >> >> >> >> >> >>> Where spark engines gain-- >>> >>> Lower internal friction (the cross-over point where efficiency gains from >>> higher compression/expansion ratio are actually CANCELLED OUT by increases >>> in internal friction happens somewhere in the 11.5 to 13.5 :1 compression >>> ratio range. ) >> >>If this were the case, then why would we use diesels at all? Surely this must >>be the case at a given rpm, where the frictional losses overcome increased >>power? >> >> >> >>> A much more efficient thermodynamic cycle. >> >>You said above "Thermal efficiency depends upon the PEAK TEMPERATURE >>reached during th cycle and upon the effective EXPANSION RATIO which is >>available during the power stroke of the cycle." > > Being that a diesel sees >>greater pressure and temperature, > >No, it does not!! > >A diesel sees a higher pressure at the top of its compression stroke than a >spark (Otto) engine does, but then burns its fuel at a nearly CONSTANT >pressure. Because it cannot burn at stoichiometric, and because it burns at >constant pressure, its peak temps are not as high! > >An Otto cycle engine burns its fuel at a nearly constant VOLUME, and at an >approximately stoich a/f ratio--therefore its peak pressure and temperature >go quite a bit higher than a diesel's do!!! > >These facts are exactly why an Otto cycle is inherently more efficient than >a diesel cycle!! > > wouldn't that neccessarily mean that it has a >>more efficient thermodynamic cycle? > >See above. The difference between constant pressure and constant volume >burning is the reason for the difference. > >Regards, Greg >> >>James Ballenger > > > ------------------------------ Date: Sat, 1 May 1999 19:24:07 -0700 From: "Howard Wilkinson" Subject: Re: Fuel injection plugs Espen: This of course has been tried and is not very successful. A more ideal solution might be something akin to the variable displacement engine built by Sandia Labs of Sandia New Mexico a number of years back. Idlers were used with a pivot point which could be varied and resulted in variable stroke which controlled power output..... the mechanism is somewhat similar in principle to how a Vice Grip adjustment works. I opened a Diesel injector pump of ancient vintage from an old motor grader and found exactly the same mechanism used to vary stroke on the injector pistons. The most reasonable way to control engine power output is by gearing so that RPM is controlled by load. A continuously variable transmission system could allow an engine to operate at full throttle all the time except at idle when it would need to be throttled. Allowing the engine to always operate at WOT would greatly increase efficiency. H.W. - -----Original Message----- From: Espen Hilde To: diy_efi@xxx.edu Date: Thursday, April 29, 1999 3:38 AM Subject: Re: Fuel injection plugs > >I tought the bennefits from diesel was the fact that its run under full >compression during part trottle.making for a compleat and fast burn. >The down side is that the exess air is cooling the combustion . >a gasoline engine on part trottle is run at low compression (less air) >the burn is slower ,we have to try to compensate with more ign.advance, >and gets more negative work done and expose the internals of the engine >with heat for a longer period.(low rpm, high advance =long time period for >negative work) >The cars are run at part trottle most of the time :-).......exept from some >folks >like myself trying to be effective....(scratching my speed itch) >We are running ineffichent engines all of us that uses gasoline ,most of >the >time when we are cruising at part trottle.This is really not acceptable.We >are accepting it because at low output the engine is not using that much >fuel >so a increase is not that much. >One way to solwe this is to cut cylinders.Making it possible for the >cylinder to operate closer to max torque where its most effective. > Espen Hilde > > ------------------------------ Date: Thu, 29 Apr 1999 22:25:15 -0400 From: James Ballenger Subject: Re: Fuel injection plugs steve ravet wrote: > > This can't be right, "If the volume of a system (such as a gas) is held constant, > > that system can do no work." That being said, a constant volume reaction would do > > no net work. > > The spark engine burns it's fuel much faster than the diesel engine. It > burns fast enough that it's simplified to a constant volume compression > because it burns while the size of the combustion chamber is not > changing size that much (right around TDC). The volume then changes of > course, when the piston moves down under the pressure of the hot burned > mixture. That's where the work comes from. The whole cycle isn't > constant volume, just the part where the heat is added. > > The diesel engine injects and burns fuel during the whole power stroke. > While the fuel is burning and trying to raise pressure, the piston is > moving down and releasing pressure. It's modeled as a constant pressure > expansion. > > --steve Thanks steve, a very good explanation that made sense. It seems that, technically, the work is still governed by the compression ratio because work is still dependant on the increase in volume. Though technically, I can push against a 2 ton rock all day long and accomplish no work though I would be damned tired. James Ballenger ------------------------------ Date: Thu, 29 Apr 1999 22:33:27 -0400 From: James Ballenger Subject: Re: Fuel injection plugs Greg Hermann wrote: > The diesel cycle is less efficient than the Otto--their higher compression > (really expansion) ratio brings some of this back. The fact that they have > no pumping losses at part throttle is the big one behind why they get > better mileage in everyday driving. I dunno. If a car gets better mileage out of the car, then it means it is getting more energy out of the energy available, therefore better efficiency. Does anybody have combustion temperatures and mean operating temperatures of a diesel vs a gas engine? I think the diesel runs hotter consistently and therefore acheives better thermal efficiency, but in any case there has to be a reason all the references I can find quote the otto cycle as being 20-30% efficient while the diesel is 25-40%. After finals (2-3 weeks), I will come back and do a little research, but until then I will sit stubbornly on my diesel throne. James Ballenger ------------------------------ Date: Thu, 29 Apr 1999 22:47:49 -0400 From: James Ballenger Subject: Re: Fuel injection plugs Howard Wilkinson wrote: > The most reasonable way to control engine power output is by > gearing so that RPM is controlled by load. A continuously variable > transmission system could allow an engine to operate at full throttle > all the time except at idle when it would need to be throttled. > Allowing the engine to always operate at WOT would greatly increase > efficiency. H.W. Ok, I know this isnt right. If we had continously variable transmissions, we would be running them at peak torque not at wot. VE is greatest at peak torque, the reason we rev engines higher to acheive high horsepower is to combat inefficient gearing. At wot, there is significantly reduced ve and not enough time to get good mixture and combustion, therefore lower torque. The reason this is an asset is because it produces more torque per unit time, ie power. With a continuously variable transmission we could run the engine all day long at peak torque and get double or triple the gas mileage, more power, and reduced wear. Again, im just a student so tell me where i goofed but I have discussed this with others before and feel somehat confident that this is right. James Ballenger ------------------------------ Date: Thu, 29 Apr 1999 21:56:30 -0400 From: "Gary Derian" Subject: Re: Fuel injection plugs No. A Diesel doesn't have more torque. Gary Derian > > > > >The diesel engine injects and burns fuel during the whole power stroke. > >While the fuel is burning and trying to raise pressure, the piston is > >moving down and releasing pressure. > > > >--steve > > > > > > So, would it be safe to deduce that these specific differences are the reason > a diesel has much higher torque output than a similar sized gas engine? > > Harold ------------------------------ Date: Fri, 30 Apr 1999 00:36:20 -0400 From: Raymond C Drouillard Subject: Re: Fuel injection plugs I like that idea. A variable displacement hydraulic pump at the engine and four variable displacement pumps (one at each wheel), along with an accumulater would allow you to size the engine for the maximum sustained load (say 100 MPH up a 7% slope fully loaded). Size the accumulater so that it can store enough energy to accelerate the vehicle's mass from 0 to 100 MPH. Design the control program to vary the displacement of the pump so that the engine is always at WOT. Also, keep the accumulater just full enough to accelerate from the current speed to 100 MPH. That way, there will be enough room left in the accumulater to absorb all of the vehicle's kinetic energy for regenerative braking. Ray Drouillard PS I really hit to comment that my dad used to use an engine called a "Waterloo Boy", which was a hit-and-miss engine. It had a governer that would cut fuel flow and spark above a certain RPM so that the engine would only fire when it got slow enough to need it. It's an interesting design, and fun to watch (and listen to) PUT na na na PUT na na PUT PUT PUT na na na na... The more you load it, the more it fires. On Sat, 1 May 1999 19:24:07 -0700 "Howard Wilkinson" writes: >Espen: > This of course has been tried and is not very successful. A more >ideal solution might be something akin to the variable displacement >engine built by Sandia Labs of Sandia New Mexico a number of years >back. Idlers were used with a pivot point which could be varied and >resulted in variable stroke which controlled power output..... the >mechanism is somewhat similar in principle to how a Vice Grip >adjustment works. I opened a Diesel injector pump of ancient vintage >from an old motor grader and found exactly the same mechanism used to >vary stroke on the injector pistons. > The most reasonable way to control engine power output is by >gearing so that RPM is controlled by load. A continuously variable >transmission system could allow an engine to operate at full throttle >all the time except at idle when it would need to be throttled. >Allowing the engine to always operate at WOT would greatly increase >efficiency. H.W. > >-----Original Message----- >From: Espen Hilde >To: diy_efi@xxx.edu > >Date: Thursday, April 29, 1999 3:38 AM >Subject: Re: Fuel injection plugs > > >> >>I tought the bennefits from diesel was the fact that its run under >full >>compression during part trottle.making for a compleat and fast burn. >>The down side is that the exess air is cooling the combustion . >>a gasoline engine on part trottle is run at low compression (less >air) >>the burn is slower ,we have to try to compensate with more >ign.advance, >>and gets more negative work done and expose the internals of the >engine >>with heat for a longer period.(low rpm, high advance =long time >period for >>negative work) >>The cars are run at part trottle most of the time :-).......exept >from some >>folks >>like myself trying to be effective....(scratching my speed itch) >>We are running ineffichent engines all of us that uses gasoline ,most >of >>the >>time when we are cruising at part trottle.This is really not >acceptable.We >>are accepting it because at low output the engine is not using that >much >>fuel >>so a increase is not that much. >>One way to solwe this is to cut cylinders.Making it possible for the >>cylinder to operate closer to max torque where its most effective. >> Espen Hilde >> >> > ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866] ------------------------------ Date: Fri, 30 Apr 1999 00:53:04 -0400 From: Raymond C Drouillard Subject: Re: Fuel injection plugs On Thu, 29 Apr 1999 22:47:49 -0400 James Ballenger writes: > > >Howard Wilkinson wrote: > >> The most reasonable way to control engine power output is by >> gearing so that RPM is controlled by load. A continuously variable >> transmission system could allow an engine to operate at full throttle >> all the time except at idle when it would need to be throttled. >> Allowing the engine to always operate at WOT would greatly increase >> efficiency. H.W. > > Ok, I know this isnt right. If we had continously variable transmissions, >we would be running them at peak torque not at wot. VE is greatest at peak >torque, the reason we rev engines higher to acheive high horsepower is to combat >inefficient gearing. At wot, there is significantly reduced ve and not enough >time to get good mixture and combustion, therefore lower torque. The reason >this is an asset is because it produces more torque per unit time, ie power. >With a continuously variable transmission we could run the engine all day long >at peak torque and get double or triple the gas mileage, more power, and reduced >wear. Again, im just a student so tell me where i goofed but I have discussed >this with others before and feel somehat confident that this is right. > >James Ballenger > Don't make the mistake of getting volumetric efficiency mixed up with engine efficiency. Engine efficiency is work in / work out. VE is air in / (.5 * displacement) (for a four-cycle engine). Torque is highest at the highest VE because you can get more fuel in for each revolution of the crank. Power is highest at the point where you can get the most fuel per unit time. If you are running at the highest torque point (max VE), you have to throttle it down to reduce power. This throttling, of course, reduces VE to the point where you get the desired power level. Of course, this increases pumping losses. A more efficient way to reduce the power level is to reduce the engine speed to below max torque. You will have about the same amount of air per unit time, but more air per revolution. Actually, you will have a little less air per unit time because it'll be running more efficiently. It won't have to do as much pumping. Other benefits are less wear and tear, lower windage losses in the crankcase, lower losses at the oil pump, etc. Ray Drouillard ___________________________________________________________________ You don't need to buy Internet access to use free Internet e-mail. Get completely free e-mail from Juno at http://www.juno.com/getjuno.html or call Juno at (800) 654-JUNO [654-5866] ------------------------------ Date: Thu, 29 Apr 1999 23:24:50 -0700 From: Aaron Willis Subject: Re: Fuel injection plugs > The most reasonable way to control engine power output is by >gearing so that RPM is controlled by load. A continuously variable >transmission system could allow an engine to operate at full throttle >all the time except at idle when it would need to be throttled. >Allowing the engine to always operate at WOT would greatly increase >efficiency. H.W. > LOL...maybe that's why I get 19mpg whether I floor it or cruise... Aaron Willis ICQ #27386985 AOL IM: hemiyota http://surf.to/garage-te51 Garage TE51 International ------------------------------ Date: 30 Apr 99 19:51:34 +1200 From: "Tom Parker" Subject: Re: Direct Injection Howard Wilkinson wrote: > I suspect that we are comparing apples to oranges here. The >engines you are speaking of are extreme high performance supercharged >engines, and I suspect that direct injection was a strategy to help >combat detonation / as was the water injection system common on WW2 >aircraft. The problem with direct injection which resulted in the use >of two injectors (not the Orbital system) was atomization was not as >good as with port injection resulting in less max power output. I always thought that the advantage of the Daimler Benz WWII engine was that its fuel injection system worked when you went into a dive, while the SU caburettors of the Rolls Royce would starve momentarily due to some sort of gee force effect. The fuel injection was also less likely to catch fire... 1937 Damiler Benz 601 A 1100hp, 1344lb 1940 Rolls Royce Merlin Series II 1030hp, 1335lb (From Fighter, by Len Deighton) Very similar power to weight ratio. - -- Tom Parker - parkert@xxx.nz - http://www.geocities.com/MotorCity/Track/8381/ ------------------------------ Date: Fri, 30 Apr 1999 10:18:01 +0200 From: "Espen Hilde" Subject: Re: Need Fuel Injector Data Can`t anyone invent a adjustable injector.......buy one injector and thats it..... Espen ------------------------------ Date: Fri, 30 Apr 1999 10:42:39 +0200 From: "Espen Hilde" Subject: Re: Fuel injection plugs Hi! I agree with using a variable transmition to keep the rpm at max torque but we have to have a variable size engine to, to get max torque we have to have wot.if we drive at wot the output will be to high for our use. Variable stroke is a help but it will be a ineffichent combustion camber with the short stroke and the compression ratio will not be good still running wot. VW made a variable compression ratio combustion camber, dont ask me how they did it.....variable combustion camber and variable stroke would do the trick .....easy uh....Ore several independant engines coupled together Espen - ---------- > From: James Ballenger > To: diy_efi@xxx.edu > Subject: Re: Fuel injection plugs > Date: 30. april 1999 04:47 > > > > Howard Wilkinson wrote: > > > The most reasonable way to control engine power output is by > > gearing so that RPM is controlled by load. A continuously variable > > transmission system could allow an engine to operate at full throttle > > all the time except at idle when it would need to be throttled. > > Allowing the engine to always operate at WOT would greatly increase > > efficiency. H.W. > > Ok, I know this isnt right. If we had continously variable transmissions, > we would be running them at peak torque not at wot. VE is greatest at peak > torque, the reason we rev engines higher to acheive high horsepower is to combat > inefficient gearing. At wot, there is significantly reduced ve and not enough > time to get good mixture and combustion, therefore lower torque. The reason > this is an asset is because it produces more torque per unit time, ie power. > With a continuously variable transmission we could run the engine all day long > at peak torque and get double or triple the gas mileage, more power, and reduced > wear. Again, im just a student so tell me where i goofed but I have discussed > this with others before and feel somehat confident that this is right. > > James Ballenger ------------------------------ End of DIY_EFI Digest V4 #251 ***************************** To subscribe to DIY_EFI-Digest, send the command: subscribe diy_efi-digest in the body of a message to "Majordomo@xxx. 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