OK guys! This is a great thread. I’m gonna get a bit techo here, but fear not, I write well and I’ll keep it interesting the whole way thru.
The real critical issue with an internal combustion engine is this - what is the peak energy conversion efficiency obtained when liberating the potential energy within fuel and then converting that into mechanical or ‘kinetic energy’.
Some of the threads above touched on the subject - and remember, Newton’s Third Law states that all energy is maintained - if only placed else where in the form of heat.
It turns out that even the most technologically advanced internal combustion engine is lucky to convert greater than 38% of it’s fuel into at-the-crankshaft horsepower. Everything else is lost purely to the cooling system which attempts to prevent the engine block turning into a lump of molte metal. And it would you know - gasoline in particular burns at a hot enough temperature to melt almost any metal. Ethyl Alcohol burns rather at lower temp but is less powerful as a result.
In Formula One, they have a really unique measurement which is of vital interest here in this article. They call it the specific power consumption measurement and it works thus - the number of grams of gasoline burnt per horsepower per hour during engine operation. Obviously, the higher the engine rpm, the greater the horsepower, but the specific power consumption figure does not.
Apparently, in 1982 when turbos were really kicking in, Ferarri were consuming 310grams per horsepower per hour. They did this because they had to run their engines incredibly rich in fuel air mixture to keep the engine temps low enough to stop them from self immolating. The heat sink of the turbos was murder I’m told. Now extrapolate that figure to a circuit like Monza. (I’m getting to a real good point here by the way). At Monza, the race ran for 1hr20mins in 1982 - that is, 1.33 hours. (roughly)
The Ferrari engine in 1982 produced 650bhp from a 1.5 litre turbocharged v6 - pretty god I think you’d agree. At 310 grams per hp per hour, that was 650 x .310kgs of fuel burnt per hour. That is, 210kgs of fuel! And the race ran for 1.33 hours. Those poor Ferraris which weighed only 600kgs at the time without fuel had to carry at least 250kgs of fuel to finish that race! Almost half their weight again in fuel… no wonder their lap times got lower as the race proceeded. Remember, back then, no fuel stops…
So… then, as the 1980’s wore on, fuel consumption rules were introduced into F1 - something which left everyone aghast at the time - but it was done to stop some engine manufacturers just running their engines at obscenely rich levels and thereby driving around in fuel bombs. So, the engine manufacturers introduced amazingly intricate engine management systems along with telemetry where they could ‘tune’ the engine in mid flight to meet the fuel restrictions. By the way, the weight limit was 220kgs for the race, so it was still PRETTY obscene how fuel consumptive they were.
Nonetheless, by the end of 1988 - the last year of the turbos - Ferrari had dropped their specific fuel consumption from 310 grams per hp per hour to just 205 grams - a truly impressive reduction in consumption - and yet, their engines were now producing close on 800 hp apparently.
Conversely, in passenger cars, rare is the road car capable of getting under 300 grams per hp per hour. They are very innefficient compared to an F1 engine - at least in terms of liberating potential energy and turning it into mechanical movement. Also, rare is the road car which is capabale of rising above 32% liberation per litre of fuel burnt. This compares to race engines which nudge 38%. The rest is lost purely to heat.
So how do F1 engines do it? Simple - they run very, very hot with oodles of research into lubricants which function at such high temperatures. The hotter an engine runs, the less energy is lost to the cooling system - thereby leaving more behind for ‘mechanical energy’.
We naturally worry immensely about a road car running hot - it usually signals a big maintenance bill just around the corner, but in racing, hot is good. Indeed, most F1 engines have pre prgrammed computer warm up routine where the engine just does weird rev patterns for 15 minutes after starting even before turning a wheel.
In summary - the measurement that REALLY counts - the one which truly demonstrates how advanced your engine is - is the ‘specfic fuel consumption’ measurement - that is, grams per horsepower (kw if you’re metric) per hour. This is the one that counts. Then, the only other issue is how much horsepower do you need? The less horsepower required, the lower the overall consumption over a given distance.
Obviously, a Mack Truck needs greater horspower over a 100 mile journey say than a moped because it has massive amounts greater friction and wind resistiance.
Conversely, a car which is doing 220kph also needs massive horsepower to because it too has massive friction as well - this time in the form of wind resistance.
Apparently, in F1, if you lift off the the throttle at 300kph and don’t even touch the brakes, the negative retardation in speed is over -1G just due to the wind resistance of the rear wing alone - such is the downforce generated at high speed.
Thanks for reading this far guys. I really love this subject - even though I’m actually a database designer by trade!
