Much has been made of the incredible efficiency of the current generation of hybrid power units used in Formula 1. There has been some discussion in the comments of some of the recent articles here about how the efficiency figure was calculated. Simplistically, this is just the maximum power delivered by the power unit divided by the maximum power available from the fuel used.
The technical regulations specify the fuel that is to be used:
19.1.1 The purpose of this Article is to ensure that the fuel used in Formula One is petrol as this term is generally understood.
19.1.2 The detailed requirements of this Article are intended to ensure the use of fuels that are composed of compounds normally found in commercial fuels and to prohibit the use of specific power-boosting chemical compounds.
While the regulations do not specify the maximum energy contained within the fuel, and I am sure that the individual fuel and lubricant suppliers will be working hard to formulate fuels that deliver that little bit extra performance, we can make an estimate based on the energy within the commercially available fuel that we put in our cars. An internet search gives a range of values, these range from 36.4 – 49.6 MJ/kg of gasoline. I am making an assumption that the fuel used in F1 will be at the top of this range (although this figure was for aviation fuel, which has an energy density greater than the fuels used for road vehicles).
The maximum flow rate of the fuel is limited by the regulations to 100 kg/hour, that is 0.027778 kg/second. Multiplying this rate by the energy density gives the maximum power within the fuel as 1,377,778 Watts. With 745.6999 Watts to a brake horsepower, that is 1847.63 bhp.
Mercedes has recently stated their intention of having 1000 bhp from their 2018 power unit, that would give them an efficiency of 54.12%. The same article states that Mercedes’ first hybrid power unit achieved an efficiency of 44%, that would equate to a power output of 813 bhp. A proportion of this maximum power is produced by the Motor Generator Unit – Kinetic (MGU-K), this is limited by the regulations to 120 kW (160.9 bhp). This is using the stored energy recovered from braking from the MGU-K or from the exhaust energy recovered from the MGU-H. Even during those portions of the lap when the stored energy is exhausted, the 2018 Mercedes will be producing 839 bhp, giving an efficiency of 45.41%, which is still 10% better than the 35% efficiency of the current non hybrid road cars.
With fossil fuels limited, the drive for efficiency will help the long term future of the sport. While many countries have long term plans to eliminate petrol and diesel engines from their roads, hopefully racing will continue in some form to use fossil fuels if only for historic classes. What do you think, is efficiency worth pursuing? Let me know in the comments.