fuel efficiency changing from small blocks to big blocks?

mercedes did tests some years ago with different size engines moving the same car technology being the same its the weight that mostly determins fuel burn and not cubes

 

weight and aero drag in a car
weight and water drag in a boat which are linked together.
water being more of a drag than air by large factor.

 

Translation:

The alkanes, parrafinics, olefins, and others are the 'neutral hydrocarbons' I mentioned. That leaves the 'aromatics' (mostly toluene and to a lesser extent, xylene) and the 'napthenics' to do the heavy lifting. These give you most of the basic octane and energy density you need while the others are blended to reduce the octane of toluene to bring it into spec without increasing the 'octane sensitivity' too much. This is especially a big problem with turbo/supercharged engines where you wind up with a big split between 'research' (R) compared to 'motor' (M) octane ratings. Nobody wants to use 'oxygenates' other than the 'exotics' (like nitropropane) because they kill energy density. The mention of manganese near the bottom is there to prohibit MMT(Methylcyclopentadienyl manganese tricarbonyl) which, like TEL(Tetra-ethyl lead), boosts octane and provides scavenging of free radicals that both attack engine components and promote detonation.

The numbers with the percentages are all about concentration limitations on specific 'species' or 'isomers' of various hydrocarbons. This part gets very technical, but keep in mind that even a substance like toluene is not a 'monolithic' substance as there are several different molecular configurations (isomers) that all qualify to be called 'toluene', and those numbers are calling out the mix of the different isomers that is allowed under F1 rules for a given hydrocarbon group.

Jimbo

 

Many thanks,
So with the above restrictions how different can they formulate this compared to EU pump gas considering they hold you at EU RON/MON numbers.
Cheers
Powerabout

 

The race day formulation will have the lowest 'octane sensitivity' and the fastest burn possible, and highest octane rating allowed under the rules, without concern about either cost or longevity of the basic parameters, since a new batch can presumably be mixed before each race. Some of these compounds can be WAY more expensive to fraction or synthesize than others, so they don't appear in any great quantity in street gas, even if they are the cat's meow as a fuel component.

Jimbo

 

Jimbo1490

My mate tells me you can stilll get 110-130 in OZ from Shell, BP and Mobil
Thats what he sticks in his Lancair.

Elf make most of the race fuel in OZ and have a very informative web site
http://www.racefuels.com.au/

Cheers

Cheers

 

interesting read Jim
have I ever mentioned I suspected you worked for the oil and gas industry at some point

anyway
dam impressive answer
B

 

LOL Jimbo,
I wish I knew what you have forgotten.

 

heres a bit from Shell.com It explains what happened to 130..just the name
http://www.shell.com/home/content/aviation/products_and_services/products/fuels/avg

History of AVGAS Grades

Avgas is gasoline fuel for reciprocating piston engined aircraft. As with all gasolines, avgas is very volatile and is extremely flammable at normal operating temperatures. Procedures and equipment for safe handling of this product must therefore be of the highest order.

Avgas grades are defined primarily by their octane rating. Two ratings are applied to aviation gasolines (the lean mixture rating and the rich mixture rating) which results in a multiple numbering system e.g. Avgas 100/130 (in this case the lean mixture performance rating is 100 and the rich mixture rating is 130).

In the past, there were many different grades of aviation gasoline in general use e.g. 80/87, 91/96, 100/130,108/135 and 115/145. However, with decreasing demand these have been rationalised down to one principle grade, Avgas 100/130. (To avoid confusion and to minimise errors in handling aviation gasoline, it is common practice to designate the grade by just the lean mixture performance, i.e. Avgas 100/130 becomes Avgas 100).

Some years ago, an additional grade was introduced to allow one fuel to be used in engines originally designed for grades with lower lead contents: this grade is called Avgas 100LL, the LL standing for 'low lead'.

All equipment and facilities handling avgas are colour coded and display prominently the API markings denoting the actual grade carried. Currently the two major grades in use internationally are Avgas 100LL and Avgas 100. To ease identification the fuels are dyed i.e. Avgas 100LL is coloured blue, while Avgas 100 is coloured green.

Very recently a new Avgas grade 82 UL (UL standing for unleaded) has been introduced. This is a low octane grade suitable for low compression engines. It has a higher vapour pressure and can be manufactured from motor gasoline components. It is particularly applicable to those aircraft which have STCs to use automotive gasoline.

******************************************************
so 100LL is new and 100/130 is now called 100
just checked the ozzie site and it says as above and the data sheets says about 100;

The combustion performance is equivalent to Avgas 100 LL. Avgas 100
has a maximum lead content of less than 0.85 gm/ litre. Avgas 100 is also known as
Avgas 100/130.

Is .85 high or low compared with the old pump gas?

 

" They just have better effiency compared to lower compression gasoline engines."

Unless the low CR was intentional to use dual turbos with waste gates to create loads of power as required or great economy..

FF

 

FF
what was the question you just answered?

 

All else being equal, you will lose fuel efficiency going to a larger displacement engine. The boat same torque will still be required at 3500 RPM, but the larger engine will operate at lower effective pressure (torque/volume), which implies a lower manifold absolute pressure, which means a higher manifold vacuum. The manifold vacuum is a significant source of loss in an internal combustion engine, particularly at light loads. Now since you have a larger engine you can use a higher compression ratio, and maybe make back some of your fuel efficiency loss.

 

Matt,
Would you mind explaining in more detail the relationships between vacuum, effective pressure, absolute pressure, etc. I feel like I am on the verge of an aha moment but I am not quite getting it.

 

Matt,

You are correct in noting that the pumping losses are higher for the larger engine if you run it at the same speed. But you are assuming that you wouldn't change the props at the same time, which directly effects the pumping losses.

If you have more torque you can (and should) also increase the prop pitch and slow down the engine. While it won't make up for all of the effects of the displacement increase (the displacement increase is linear and the speed increase is a square root function, so you can't change the gearing as much as you would if the speed increase was linear, so don't get it all back) a taller prop pitch will reduce the pumping losses and help with the part power fuel economy.

You are left with two effects, the higher weight effect on speed and drag, and somewhat higher pumping losses (approximately 1/2 of what they would be if you didn't change the props). Both are real, but they aren't a huge impact on fuel economy, you are probalby going to be within 10%, or maybe even less.

The difference is that you have a pair of engines that aren't being loaded as highly, so there are payoffs in terms of engine life, and if you want higher speed you have that too if you want to bend the throttles.

 

What Matt is describing are called pumping losses. With a gasoline engine you control the power output with a throttle plate. That means before the air gets to the cylinders it gets sucked past a throttle plate that (at part power) isn't open all the way. So the engine is really getting it's air from a low pressure intake manifold. To exhaust the air, you have to pump it from the lower pressure intake manifold out to the atmosphere. At idle the pumping losses are 100% of the load. As the engine speed increases the engine wants to pump more air, but if you don't want much power you have to pump the air that you do need back up to atmospheric pressure to get it out of the engine.

This is why many cars have a really tall gear ratio so that they are barely turning over on the highway. My Corvette for example is only turning over at 1700 rpm at 70 mph. This tall gear ratio allows a wider throttle opening at lower speed, and the net effect is better efficiency. A Corvette six speed typically gets about 30 mpg at 70 mph, which is, for a car of that capability is most impressive.