Larger displacement for better mpgs?

[kachok25]

Intresting tid bit of info, I just did a few mathmatical equations, and even with it's insane 6 inch stroke, this engine could run aprox 5000 rpms without exceding the internal g-forces of other production engines! 6"x 5000rpm x2cycles=5000ft per min. I would probably have to go with a long rod design to deal with those rpms though and that would slightly compromise low end torque, but a good thing for engine life (less laterial force aginst the rings and pistons, and less stress on the wristpins and just about any other moving part because of the more gradual g-forces at TDC and BDC) the higher RPM would allow to push the redline power to 800-900HP!! OK without advanced VVTi and variable length intake runners maby more like 700hp but that is still major kick.

[drunken monkey]

any chance of showing us the maths you have done and what they mean and relate to, so that those of us who does know a bit about the mechanics of these things can take a look and see what you're doing?

[Dyno247365]

I never thought of the equations dealing with bore, stroke, or even the size of the engine compared to its fuel mileage. A car with a more powerful engine gets you to where you are going quicker, which means it travels more miles in a shorter time then a less powerful engine. The only really problem I see is the speed limit. It won't matter how fast your car goes if you're both at a constant speed (65mph) and the engine built to conserve energy (and fuel) wins.

[kachok25]

Originally Posted by drunken monkey

any chance of showing us the maths you have done and what they mean and relate to, so that those of us who does know a bit about the mechanics of these things can take a look and see what you're doing?

OK here we go surrface to valume ratio 7(bore) x3.14 (pie)=21.98x6(stroke)x4(cylinders)=527+(3.5x3.5)3. 14x2x4 (surface area area of piston and combustion chamber) Total 834 sq in for 923 cu in. The importance of that is that with lager cylinders and more stroke the surface to volume ratio is decreased which helps with fuel effecency since there is less heat loss through the cylinder walls, a typical V8 has aprox twice that surface to volume ratio.
As far as the RPM goes take your stroke (6") times your cycles per rotation (2) times your RPM devided by 12 (12"=1foot) and you have your piston speed in this case 5000 FPM (feet per min). 6600 FPM is where things usualy start to come unglued, depending on what material are used for the internals. As far as the rod to stroke ratio, Longer rods mean less G-forces at Top dead center and bottom dead center TDC and BDC, 1.5-1.8 rod to stroke ratio is pretty standard.
Are there any other equations you are looking for??

[kachok25]

Originally Posted by Dyno247365

I never thought of the equations dealing with bore, stroke, or even the size of the engine compared to its fuel mileage. A car with a more powerful engine gets you to where you are going quicker, which means it travels more miles in a shorter time then a less powerful engine. The only really problem I see is the speed limit. It won't matter how fast your car goes if you're both at a constant speed (65mph) and the engine built to conserve energy (and fuel) wins.

There is more to it than which engine will get you there faster, I already pointed out several examples in my first post, lower engine speeds mean less friction, less friction means better effecency, better effecency usualy means better MPG. If a 1.3L Yaris could cruse highway speeds at 1600 RPM like a Z28 you would have fuel effecency approching the tripple digits, but the 1.3L engine does not make enough low end torque to do that. Even with Toyota engineering a 1.3L engine could not push a nearly two ton car while getting 28mpg, it would have to work way too hard (4000+RPM), but a 5.7L 300hp LS1 can. What I am attempting to do is to step up the engine size even more and reduce the engine rpm at cruse, basicly make an engine that could push a car at highway speeds at below 700 RPM, it sounds really weird but if you look at the physics behind it, it makes alot of sence, a large engine can opperate with less friction at 700 rpm than a small engine can at 3600 RPM (in the yaris or XAs case) Rember friction is not a linier equation, if engine speeds double friction quadruples!

[drunken monkey]

i was thinking more along the lines of the real spoddy bits of maths dealing with masses, inertia, vibrations, amount of fuel needed per cycle that sort of thing.
you started this thread by stating a "want" for a more efficient engine but so far, i don't really see anything that follows on from this apart from mentioning the theoretical reduction of loss of energy through heat.

where are you getting that your idea would more fuel efficient than a "regular" engine?

[kachok25]

Originally Posted by drunken monkey

i was thinking more along the lines of the real spoddy bits of maths dealing with masses, inertia, vibrations, amount of fuel needed per cycle that sort of thing.
you started this thread by stating a "want" for a more efficient engine but so far, i don't really see anything that follows on from this apart from mentioning the theoretical reduction of loss of energy through heat.

where are you getting that your idea would more fuel efficient than a "regular" engine?

I don't have all the mathamatical equations, that is why I started this thread, if I had all the anwsers I would not humble myself and ask for anwers, if you know anything I don't please let me know. I have a pretty good idea as far as things like inertia goes, but this is so upscale from from anything of its kind ever built that I don't know for sure, I would assume that a piston with twice the mass as a typcal 4" piston with twice the barring area and twice the structural strength could support the same g-forces, but again I am not sure maby there is a variable that I overlookerd, as far as effecency goes I have mentioned plenty of things other than surface to volume ratio, like swept area friction, valvetrain friction, Using direct injection to reduce the required fuel to air ratio. None of this is crazy science fiction it is all based on pre-existing ideas and facts, all put togeather into one concept. I can show you the basis for any one of the facts that I mentioned. The most important factors I am looking for are how much energy the avrage internal combustion engine looses through swept area friction, valvetrain friction, and thermal loss through the internal surface of the engine. Any additional factors you know of I would love to hear about them.

[drunken monkey]

i'm not saying this is far fetched science fiction; after all, they used to make 27 litre V12s pumping out 1000+ bhp easily 60+ years ago.
it's just that the first thing that comes to mind is that thermal efficiency doesn't automatically equal good fuel economy.
by the same token, super efficient use of fuel in modern engines also doesn't automatically equal good thermal efficiency or fuel economy.

first thing's first.
what kind of efficiency are you looking at specifically?

[kachok25]

Originally Posted by drunken monkey

i'm not saying this is far fetched science fiction; after all, they used to make 27 litre V12s pumping out 1000+ bhp easily 60+ years ago.
it's just that the first thing that comes to mind is that thermal efficiency doesn't automatically equal good fuel economy.
by the same token, super efficient use of fuel in modern engines also doesn't automatically equal good thermal efficiency or fuel economy.

first thing's first.
what kind of efficiency are you looking at specifically?

Extreme (highway speed) fuel effecency. And or marine crusing speed. Combining high thermal effecency with modern direct fuel injection. All in one neat package that would provide cuting edge proformance witout sacraficing economy. Most importantly I wanted to find the upper limits of thermal effecency in an automotive sized engine. Although I admit 15.1L is a touch excesive, but to achieve max thermal effecency I would need a low surface to volume ratio platform, and the reason I chose this size is it has aprox 1/2 the surface to volume ratio and swept ares (per cu in) as your avrage V8.

[KiwiBacon]

Originally Posted by kachok25

A few things you are not taking into consideration standby losses are reduced with a direct injection (remember the 30:1 AF ratio) Also remamber we are in the age of hybrids once the battery is charged who is to say it wont have an auto shut off, and just run it on the battery for a while, but even with regular port injection and no hybrid system I would put it aginst any proformance minded 4 cylinder anyday, for effecency or proformance I would bet the larger engine would stomp a mudhole in it in every event exept for standby fuel consumption, and you know what I could live with that. I don't know about you but I don't spend much time at a dead stop. During my hour drive to work everyday I probably do not spend any more than three munites at a stop.

Standby losses are the amount of power it takes to turn the engine. They are not changed by direct injection, battery charging or any other such factors.

Anything a petrol can gain by using hybrid drive, a diesel can also gain.

You may not spend much time at a dead stop, but the average car engine spends almost all of it's time heavily throttled. In these situations a large engine is nothing but a waste of space and fuel.

Comparing highway MPG is not the whole story. There are many standards worldwide for fuel consumption tests, a large engine will do poorly in all of them.

It takes me 15 minutes to pedal to work on a mountainbike. The same journey in a car takes 7 minutes and consumes over half a litre of petrol.

[KiwiBacon]

Originally Posted by kachok25

Intresting tid bit of info, I just did a few mathmatical equations, and even with it's insane 6 inch stroke, this engine could run aprox 5000 rpms without exceding the internal g-forces of other production engines! 6"x 5000rpm x2cycles=5000ft per min. I would probably have to go with a long rod design to deal with those rpms though and that would slightly compromise low end torque, but a good thing for engine life (less laterial force aginst the rings and pistons, and less stress on the wristpins and just about any other moving part because of the more gradual g-forces at TDC and BDC) the higher RPM would allow to push the redline power to 800-900HP!! OK without advanced VVTi and variable length intake runners maby more like 700hp but that is still major kick.

Linear speed isn't the problem in an engine revving.

Linear acceleration at the top of the stroke is.

The thermal efficiency of a petrol engine is appalling. You are flogging a dead horse. But that same dead horse is being flogged in much better ways by thousands of professional engineers world-wide.

In case you didn't realise. The thermal efficiency is very closely linked to the compression ratio. A diesel has typically twice the compression of a petrol engine.

[KiwiBacon]

Originally Posted by kachok25

As completly sweet as that is I am trying to beat that for power and fuel effecency, without the use of a turbo. With less than half the friction, and half the heat loss of a conventional V8,

Are you going to cure cancer and world hunger while you're at it?

Your goals are completely unrealistic and unacheivable.

[kachok25]

Originally Posted by KiwiBacon

Standby losses are the amount of power it takes to turn the engine. They are not changed by direct injection, battery charging or any other such factors.

Anything a petrol can gain by using hybrid drive, a diesel can also gain.

You may not spend much time at a dead stop, but the average car engine spends almost all of it's time heavily throttled. In these situations a large engine is nothing but a waste of space and fuel.

Comparing highway MPG is not the whole story. There are many standards worldwide for fuel consumption tests, a large engine will do poorly in all of them.

It takes me 15 minutes to pedal to work on a mountainbike. The same journey in a car takes 7 minutes and consumes over half a litre of petrol.

I would have to disagree with you several large engines have done well on the highway, the massive 6.0L 400hp LS2 gets 28 mpg in the 07 vette, the 5.3L V8 Chevy gets as good or better fuel ecconomy than their smaller 4.8 V8 or even their v6. I work at a GM dealership I see examples of this all the time, I got a trade in the other day a full size GMC pickup with 168,000 mile on it with a 5.3L V8 that was still getting over 23mpg without displacement on demand (it had the drivers information center with exact fuel consumption) the 4.3L v6 only gets 21 mpg so how are you going to tell me that it is not possable for a larger engine to get better fuel effecency??? There are plenty of other examples I can point out if you want me too.

[KiwiBacon]

Originally Posted by kachok25

so how are you going to tell me that it is not possable for a larger engine to get better fuel effecency???

There are thousands of engineers out there who have been working for the last 100 years to get the best possible efficiency out of the petrol internal combustion engine.

The petrol engine is so close to it's peak that there is no large gain possible.

Put those vehicles through a combined cycle fuel economy test and your results will be very very different.
The fact that the occasional owner spends all their time driving on the highway and gets good numbers doesn't matter when the same vehicle won't get 4 km/l in an urban environment.

So what if a 6.0l vette can get 28 USmpg. A smaller petrol engine in the same car could almost double that. A diesel engine in the same car would more than double that.

[kachok25]

Originally Posted by KiwiBacon

Linear speed isn't the problem in an engine revving.

Linear acceleration at the top of the stroke is.

The thermal efficiency of a petrol engine is appalling. You are flogging a dead horse. But that same dead horse is being flogged in much better ways by thousands of professional engineers world-wide.

In case you didn't realise. The thermal efficiency is very closely linked to the compression ratio. A diesel has typically twice the compression of a petrol engine.

I know that compression ratio is linked to thermal effecency, but higher compression is only part of the story if you did your reserch you would see that after 17:1 compression you actualy loose a small amount of power, that is why you see the move to turbocharged diesels running between 16.5 and 17:1 CR, but if you did your homework you would also know that with direct injection you could the same 17:1 compression as a diesel since pre ignition is not even possable with a proper setup. I never said that linear speed was a problem with engien reving I was concerned with recprocating mass, if you had actualy read my post you would know that, if you are going to make smart ass coments on someone elses idea make sure you read the idea first. As far as thousands of professional engineers world wide goes they are too blinded by pre-formed ideas of how things should be, that is why many of the great inovations come from other sources, and once the idea is proven engineers improve on it. Inventors and pioneers are not usualy engineers, but everyday people that have a great idea, yeah maby 99% of the time we are wrong, but that 1% is the next big thing. I invented two different types of the CVT transmision when I was 12 years old, (variable pully and twin cone) and my dad (a gearhead) told me that they could not work, within the next ten years both had been built and tested, one is in production and the other is in testing. So don't tell me that if an engineer did not come up with it ignore it, if a 12 year old that never drove a car can come up with an idea years before any engineers do, don't assume they are all knowing OK. Oh and in case you did not notice diesels are on the decline here in the US due to our emmissions laws. FYI do your own reserch before you bash someone elses.