has BSFC of gas engines even really improved in decades?

[stillsearching]

I'm aware that diesels have been seeming to have slow increases over time but what about common gasoline engines? Are engines of today substantially better than engines of the 1980's or even the 1960's? I'm aware of the big improvements in horsepower without affecting driveability which technology has enabled, but the few times i'd seen SFC maps for "old" technology engines they seemed to practically be the same as what they had now FIFTY YEARS LATER unless they were not really representative of either older engines or newer engines as a class of their time...

Cars have gotten better mileage due to better transmission technology, but when the original 1908 Ford Model T was reported to average 25mpg (this cheats a bit both ways and i'm aware how it isn't really a fair comparison but hear me out) i'm trying to figure out what we really are doing that much better.

Are there any credible breakthroughs on the horizon that will actually give more than just a few % increase over the next 2-3 decades? The way I see it other than compression ratio (which is all about withstanding pressures without detonation), lean burn strategies, or someone figuring out how the heck Smokey Yunick's Fiero actually worked i'm wondering whether there is anything to really look forward to in the normal Otto cycle engine. A honda civic might have 600hp in 2035 and have a 14 speed automatic but will it honestly be capable of much better MPG if put in vehicles of the same weight and aerodynamic load driven the same way under the same conditions?

[Big Dave]

In terms of improvements to absolute BSFC, I don't think there is much scope for improvement. It has often been said that gas engine technology hit the peak with Louis Meyer's engine back in 1925.

Electronic controls allow the engine to operate at near-peak efficiency over a wide range of conditions, but the peak hasn't changed since the Napier Sabre back in the 1940s.

This is why I never much worry about engine tweaks.

Aerodynamics? Yeah. Lotsa room for improvement.
Transmissions? The big enchilada in my book.
Engines? Pretty much at their peak.

[mechman600]

Originally Posted by Big Dave

Electronic controls allow the engine to operate at near-peak efficiency over a wide range of conditions...

That's pretty much it. Aside from a few percent, modern things like variable valve timing and electronics simply broaden the RPM range of peak BSFC a bit.

[AndrzejM]

Mercedes Benz had this idea to combine diesel and otto cycles together to improve efficiency of gasoline engine: DiesOtto

[RobertISaar]

a lot things along the way have been counteracting improvements to any part of the vehicle. in terms of "why hasn't MPG really improved", look to the general public and see what they're driving and how they're driving it.

since about ~1985, the scream has been for "more power at the same MPG", recently that's changed though and a few vehicles crept up to some really out of the ordinary numbers, but very few of them were sold in high numbers.

essentially, this is what people want(since it's what they keep buying), so it's what the manufacturers build. CAFE and the like are trying to artificially change consumer desires by forcing low MPG vehicles to be sold in VERY low numbers(and with a hefty gas guzzler tax) or eliminated entirely, while forcing the other vehicles to be increasingly efficienct.

another counteraction is safety... take all of the safety equipment that is beyond the ~1988 era out of a newer car and you'll have a significant difference in weight. now pedestrian safety is being factored into automotive design, likely as a detriment to aerodynamics.

there's just so many things preventing modern engines from being the non-compromising design that they could be.

[some_other_dave]

I believe that BSFC has dropped significantly since the 1960s. Innovations like variable valve timing and lift, precise fuel metering from fuel injection, direct fuel injection, and turbochargers that can be used on a daily driver have all contributed.

Consider that a 1972 Mustang 302 V8 made 140 HP (SAE Net standard). My 2012 MINI Cooper (1.6 liter, about 99 cubic inches) makes 121 HP by that same measurement scale. It also uses a whole lot less fuel to make that power. And that ignores the Cooper S and Cooper JCW, which make 181 and 200+ HP respectively.

I wonder if we can find BSFC curves or maps for some of the old-old cars....

-soD

[user removed]

Brake specific fuel consumption - Wikipedia, the free encyclopedia

Check the years of some of these engines. They go back quite a while. I think BSFC has improved generally but I also think there is a long way to go. Argonne Labs is working on getting close to 60% which is the theoretical ideal for an IC reciprocating engine.

Personally I think 60% is attainable but it will not be with a conventional powertrain. It will need to have capacitive energy storage to allow P&G (engine off) to become the operational standard. The issue is how efficient can you make the capacitive storage. It has to have very high efficiency or you lose the gains from intermittent max efficiency operation.

Engines will need to be redesigned to maximise the on-off constant load operation and many components will be unnecessary as well as other components that will be specificly engineered for a very narrow range of load operation in an all or nothing strategy. Throttle control will be eliminated altogether.

regards
Mech

[gone-ot]

BSFC technology kinda matured & peaked with aircraft engines during WWII, which were then by-passed by jets. Unfortunately, we are still driving internal combustion engines, not jets (darn you Detroit)!