Fuel thermal efficiency
Thermal efficiency is a way to measure efficiency of an internal combustion engine. Internal combustion engines in general are inherently inefficient and even an advanced modern F1 engines are no exception. They are very inefficient when it comes to converting the power available from the fuel/air mixture into power at the rear wheels. For an F1 engine this value (before 2014 technical rules change) was typically around and below 30%. This mean that if a typical F1 engine produces slightly under 560 KW (approx. 750 bhp) on the dyno, something like 1500 KW (or potentially 2000 bhp) of the energy was lost, mainly trough the heat. After 2014 rule change figure of 30% has changed, going from old internal combustion 2.6 V8 engines, naturally aspirated at about 30% thermal efficiency to 40% with new 1.6 V6 engines, and this is a huge step forward.
Meanwhile, after 2015, the technology has advanced the efficiency of engines to 47% and producing historic highs of power - and all with an ICE restricted to consuming fuel at a rate of just 100kg/hr, meaning that 50 % of the potential power than can be derived from a unit of petrol is being converted. The goal is 100% but that is far in the distance. At the outset of the internal combustion engine, efficiency of 12% was standard. Over 130 years that improved to 29%, which is where F1 V8 engines were in 2013. In the step since then, it has gone up to 50%.
The turbo hybrid V6 'power-units' introduced into F1 in 2014 are masterpieces of technology that have produced a revolutionary step forward in the performance of the internal combustion engine. In 130 years, efficiency increased from 12% to 29%, a yearly increase of 0.68%. In the 3 years F1 has these new power units, they’ve increased the efficiency near or to 50%. A yearly increase of 20%. That means the rate of progress with regards to efficiency is over 98% faster since F1 engineers have been involved.
Mercedes has dominated Formula One since the introduction of the current regulations in 2014 and for most of that period it has held a significant power advantage over its rivals. In a presentation to media at the team's engine factory in Brixworth, Andy Cowell, Mercedes engine boss explained that the current 1.6-litre V6 turbo hybrid is now producing more power than the 3.0-litre V10 Mercedes engine of 2005, in excess of 900bhp, and says there is no reason to believe its development rate will slow in the next few years.
"It's the most powerful Formula One engine [we've made] with over 900bhp. It's pretty good going from this little nimble 1.6 litre engine, but that power has been created because the efficiency has changed. We've got road-car technologies in there and new emerging technologies are in there with regard to the MGU-H."
Cowell revealed that the Mercedes power unit is now achieving more than 45 and close to 50 percent thermal efficiency, i.e. 45 - 50 percent of the potential energy in the fuel is delivered to the crankshaft, and efficiency of more than 50 percent when the ERS is operating at full power.
By comparison, the V8 engines pre-2014 achieved thermal efficiency of 29 percent and the first iteration of the Mercedes V6 turbo in 2014 managed 40 percent thermal efficiency.
Generally speaking, if you want to find efficiency in a internal combustion engine you tend to look at diesel engines on huge ships that work at 100rpm or something. They are so slow that they have very little friction and they are so steady in the way that they operate that they can be set up and optimized to work on one cycle for optimum efficiency. This one-purpose, solely-designed-for-fuel-efficiency engine work like that for days without anyone touching them and they have great big heat recovery plants the size of a house. That's the sort of benchmark for a thermally efficient internal combustion engine.
Energy lost trough exhaust constitutes a very important source of energy to tap into in order to increase the efficiency and hence the power output of the engine. To make engines more energy efficient and to have more relevance to the production car industry, FIA and the engine manufacturers agreed to change engine format for 2014 and beyond. The configuration agreed upon is a 1,600 cc -V- 90 degrees 6 cylinder engine with an REV limit of 15,000 rpm. With the desire to keep power levels similar to 2013 spec engines, turbocharging and energy recovery systems are permitted. This engines are most impressive engines in the history of the industry, with unheard of thermal efficiency figures and impressive horsepower numbers for the amounts of fuel being used.To learn more about new 2014 engines (Power Units) check my article here.
Adopting such technology in Formula One will surely go a long way to enhance the green credentials of motorsport and in addition develop a technology that will prove beneficial in road car applications.
This picture and energy path is for modern gasoline road cars. F1 car is about 25% more effective! (green part of diagram).
For example, lubrication oil heat dissipates around 120 KW of energy, water cooling system around 160 KW and hydraulics around 30 KW.
30% of remainder lost energy is lost trough exhaust and heat, while up to 10% of the available energy can be accounted for unburnt fuel. A small percentage is turned into the distinctive sound of an F1 car. And this is a difficult task as by definition noise is wasted energy, and the whole point of hybrid engines is to regenerate as much of what would traditionally be wasted energy as possible.
To dissipate this heat in surrounding air is real challenge for designers. While the heat exchangers on a racing car are extremely efficient, their ability to cool the engine is a function of the 'air-side capacity'. Essentially, how big a mass of air you can make flow through the radiator for a given area in given moment. This depends on generating high air velocities in the radiator intake ducts. However, typically, air velocity in the radiator ducts (sidepods of F1 car) will only be 10-15% of the car's velocity. So even if the car is traveling at 300 kph, the air in the ducts is probably only at 30-40 kph. This data is more or less the same for all racing cars without additional fan. For family car speed of air is even slower, but helped with cooling fan.
If designer make cooling duct intakes openings to big, that will improve cooling, but will ad to drag. If they are too small, overheating will be a problem. They must find the correct balance between cooling and aero performance because the more air they channel through the radiators, the less efficient the overall aerodynamics become. More air they channel through the radiators, less air remain for underflor, diffuser and rear wings to play with.
They can't make internal aerodynamics so clean and efficient like external one. In fact, changing between minimum and maximum cooling can reduce downforce by as much as 5%, which translates to a lap-time deficit of around 0.4s on an average circuit. Because air inlet is defined mostly during early stages of designing of an F1 car and can't be changed easily during the season (air inlet is very often designed like part of side impact area), airflow passing trough sidepods is controlled by different configurations of radiator outlet, and the F1 car has a lot of different possible configurations to cope with all kind of conditions. The configuration used at a particular circuit is defined according to the ambient temperatures, 'circuit factors' such as how much full throttle is used, and the temperature limits they can run the engine.
Typically, oil temperature is around and over 100 C and water is pressurized at 3.75 bar (limited by FIA) to allow boiling point to be pushed to around 120 C. Running these higher water temperatures means that they require less airflow through the radiators, and in this way they can improve aerodynamic performance.
This choice carry a penalty: each extra 5°C of water temperature they run, allowing the radiator outlets to be smaller, robs the engine of over 1 bhp. However, the importance of aerodynamics in modern F1 means they continue devoting significant resources and wind tunnel time to cooling and internal aerodynamics. This is better illustrated by the fact that the penalty in terms of aero efficiency they must accept for a 10°C drop in car temperatures is 80% smaller than it was just four years ago. This is proving that internal aerodynamics of an F1 car is as much important as external aerodynamics. Only we can't see that.
After 2014 engine formula change, Two separate hybrid technologies are being used in the F1 engines. One recovers energy from the rear axle during braking, stores it in a battery and reapplies it under acceleration. The second, and completely new technology, recovers energy from the turbocharger shaft and is used for two purposes. It can be applied directly to the rear wheels to boost acceleration, and it can be used to run an electric motor on the turbocharger ti spin it up so you have immediate boost as soon as the driver presses the accelerator. This almost completely eradicates the delayed throttle response inherent in turbocharger engines, which is known as "turbo lag". That's where F1 engines are road-relevant.
Combining these two hybrid technologies has meant F1 engines now have a thermal efficiency of more than 40% - better than a road-going diesel engine.