ORIGINAL: gkamysz
Ken,
Efficiency is a complex matter. Gasoline engines are more than 15% efficient. Recent Honda engines are ~33% if I remember correctly. The largest diesels in cargo ships are about 50% efficient. Compression does have an effect on efficiency but there is a point of reduced return. Injected diesels need 18:1 to allow cold starting. Spark ignition gasoline engines are limited to ~13:1 for the best designs due to fuel characteristics.
http://en.wikipedia.org/wiki/Specific_fuel_consumption
A Prius BSFC according to one link I found is 225g/kWh.
I estimate BSFC of my FS-48 conversion to be 360-380g/kWh on kerosene.
Andy, if Kelly was talking about the difference in carbs due to fuel, the real question is how much air does the fuel displace? With a 10% difference in volume comparing diesel and gasoline, this is trivial compared to methanol which requires twice as much volume and mass to equal gasoline. Since the density of methanol and kerosene are close we could say it's just the fuel air ratio. Straight methanol is 6.5:1 but I'm sure we run rich at ~5.5:1 and Kerosene should be 14.5:1, but I think we run rich near 11:1. We should be able to reduce the area of our carbs by 10% without ill effect. This doesn't consider the cooling effect of fuel evaporation. Restrictors in my opinion go back to the idea of mass flow reduction associated with the reduced RPM we run diesels at. The biggest change in carburetion is jetting changes(needle setting). Because we use needles instead of fixed jets this is a no brainer, the engine won't run unless the needle is close. The main thing is that you want o keep a certain velocity thru the venturi so that there is enough pressure differential to have good fuel draw.
I have tried restrictors in my four strokes and have not come to a definite conclusion at this point. So far I have just tried them but not evaluated the science behind it. The Enya 41-4CD has a substantial restrictor.
I was thinking the same about comparing viscosities to known lubricants. The problem is keeping the lube at engine temperature to get a meaningful comparison.
Greg,
I'm in agreement with you that automatically going to a smaller venturi for diesel isn't, shouldn't be, cast in stone. There are variables to consider, none of them it seems, predictable. My .06 and .074s don't mind the stock or even larger bore venturis. The bigger engines show signs of some compromises required. This may simply be a case where the manufacturer went way too small for likely legitimate reasons. They have to make the engine to suit all conditions and customer experience. I've been far too critical of the people who make these things, just my anal, perfectionist nature. I get it now.
The best thing is that if you have the tools, courage and capacity, JUST TRY IT. It may surprise you. While waiting for the .15 rebuild, I strayed to the glow side and discovered, by accident, but on a hunch, a fuel mix/additive that boosted performance and acceleration by a surprising amount. And this was an experiment to make up a glow fuel using locally available ingredients. Aviation oil is next to try. If it works and lubes well enough, I just may start flying .60 and up planes again. We'll, see.
Graham,
A good summation and some great links to bend the synapses into pretzels. God, I wish I had a better memory. But it's not over by a long shot. Two new ideas to try. On the bio-diesel forums, I was alerted to a product that is supposed to turn ordinary veggie oil into a fuel without the alchemy of making biodiesel.
As my experience with the virgin soy oil showed, oil will burn in our engines. Not efficiently but who knew that they would run at all. Before the taboo against electric starters was broken, yes, you could say that a model diesel will not run on straight vegetable oil. But no, as we found out, it won't START on pure veggie oil but it certainly will RUN on it. The trick is to find a combination of oil, fuel, additive and even engine design that puts it all together. Both Greg and Kelly have inspired a new experiment that involves more efficient delivery and atomization of the heavier, veggie fuel, whether it be biodiesel or straight vegetable oil. This could only be tried on a Norvel and that is next in line. First to make a number of runs on a stock engine, do the mods and repeat.
Your experience with too much ignition improver seemingly contradicts my own. I went to 10% Amsoil CB and the engine ran well enough with a much decreased compression setting. But throttling went away and never came back. There are applications where this is not an issue. Not for me. Food for thought. Need to revisit the matter.
I haven't got to the ether history link yet but it's my understanding that the anesthetic vaue of ether for surgery was known for hundreds of years but was ignored by the establishment. Much suffering in that time, going under the knife fully awake and aware. Many refused the ordeal and preferred to die. All for nothing for hunderds of years. Or so I had been told.
Off to the shop to chop alluminum.