riff_raff wrote:olefud wrote:The Wankel is out of its league for power efficiency. It might look better on power per unit mass.
olefud,
I agree, the Wankel is compact and lightweight, but has relatively poor BTE. Even though the Merc and Mazda engines were not F1 powerplants they were still dedicated race engine designs from the same time period, so I included them for comparison. I found it interesting that even a relatively "poor" F1 engine design like the Lambo V12 had better thermal efficiency than the best sports car engines of that period.
Regards,
riff_raff
The R26B rotary was at 180 kg not especially lightweight compared to other Le Mans engines of the same era.
Also, 227 g/hp-hr is 309 g/kWh and 222 g/hp-hr is 302 g/kWh; so the Lambo V12 was significantly worse than the Mercedes M119 and slightly worse than the R26B in terms of fuel efficiency. These numbers also compares well to the official numbers of the Honda RA168E turbocharged formula 1 engine of 1988; the RA168E achieved a low figure of 272 g/kWh in "economy mode" at 12 000 rpm, about 280 g/kWh at peak power speed and between approx. 300 and 272 g/kWh at full load between 7000 and 13 000 rpm. Given an energy density of 41.07 MJ/kg for the Honda race fuel the maximum efficiency was 32.2%. I would suspect that the racefuel used by the other racing engines was more energy dense. Even with a more energy dense fuel the Mercedes figure of 235 g/kWh would translate into an quite impressive brake thermal efficiency figure of 35.5%. That's not far behind say the Atkinson cycle engine found in Toyota Prius.
I would also not expect current F1 engines to beat the best engine above in terms of efficiency. Since F1 engines are still indirect injected not that much have happened since the eighties with regard to fuel and ignition control that can improve efficiency. Map based control of ignition and fuel have been used since the early eighties. Given the higher speed of the current engines they also have a massive handicap in terms of friction. Of course, if we could adapt many of the modern technologies found in current F1 engines (DLC coated pistons, separate crankcase chambers...) on one of these older design that would most likely cause a significant drop in frictional losses. Add direct injection and the engines could run a bit leaner (saving a few percent fuel) while allowing for a higher compression ratio (due to the charge cooling effect of direct injection).
