2014 Power Unit - Thermodynamics

With the introduction of Hybrid power trains for the 2014 FIA Formula 1 season, I thought it’d be the perfect time to introduce the ‘Thermodynamics’ subject, and how crucial understanding it is to a powerful, thermally efficient hybrid power train.

Thermodynamics is the study of energy. We use thermodynamics in power units to understand how to maximise efficiency. Maximising efficiency is achieved by reducing energy losses across a system.

If we maximise Power Unit efficiency in our Formula 1 scenario, we can use a lower volume (therefore lower mass) of fuel but still achieve the same levels of power output from the power unit. By reducing fuel consumption as much as possible whilst maintaining power output, it means that less fuel needs to be put into the car to complete a race distance. Less fuel means less weight, less weight equates to better lap-times from better tyre management and better power to weight ratio.

Throughout the 2014 season, FOM have treated us F1 viewers to live fuel consumption data. Every occasion that the data has been shown, we have seen that the Mercedes Power Units have used less fuel (at that particular point in the race) than their rival Renault Power Units.

There are different ways that thermodynamic calculations can be applied to a system, from Rankin cycles to PINCH technology. I won’t progress into any form of calculations because the level of understanding required! Even I would struggle to do calculations on the very complex 2014 PU!

When I refer to a ‘system’, I am talking about a cycle of some sort. For example, if I will quickly demonstrate the energy cycle of a turbocharger:

• To begin with, I’d like to add that this is not a fully accurate representation of a turbocharger system; I have drawn this diagram to demonstrate what happens in the ‘cycle’.
• The lines connecting the components together represent pipework for the working fluid, which in this case is air. Air is the fluid used in this system to produce WORK.
• The circuit is broken at stage three because the working fluid, air, is rejected from the system via the exhaust pipe. The compressor then brings clean, cold air back into the system ready for another cycle.

W = WORK (A useful form of energy we can use mechanically)

Q = HEAT FLOW

Step 1:

Cold compressed air enters the ICE combustion chamber. The combustion process adds heat into the system, Qin. This means that our working fluid has absorbed heat energy (hot exhaust gases).

Step 2:

Used gases are expelled from the ICE. Usually they would be released into the atmosphere through the exhaust pipe, but that would be very inefficient because the hot, high velocity gases still possess a lot of thermal energy. This thermal energy can be used to do something useful to increase the efficiency of the powertrain…

The exhaust gases from the ICE are sent to a turbine, the job of the turbine is to create work,         W-out by removing energy from the working fluid (exhaust gas). Can you see how we used energy that would’ve been wasted to make it into something useful?

Step 3:

The gases that spun the turbine to create work have now been discharged through the exhaust tail pipe. These gases are of lower energy which results in lower decibel level of sound as they escape into the atmosphere!

The work produced by the turbine is now used to run the compressor. The compressor compresses fresh air taken in from the air intake above the drivers’ heads, work is being put into the system,  W-in, as the working fluid (fresh air) is being compressed.

Step 4:

Pressure is proportional to temperature; therefore our compressed air (high pressure) is now also very hot. If this hot compressed air is put straight into the combustion chamber, it would result in inefficient combustion and be detrimental to the materials used for the engine’s components, so the air needs to be cooled somehow.

The intercooler cools the compressed air so that it is a suitable temperature for combustion; the engineers have to compromise intercooler size with aerodynamics. The aerodynamicists will desire small side pods, therefore small intercooler, but the engineers will want a large intercooler to increase the cooling levels of the gases.

Step 1:

The cooled compressed air is ready for combustion and the cycle continues.

Efficiency:

If this was an example of a steam power plant, the engineers would want as much W-out as possible but for the smallest W-in as possible. More W-out means that the power plant can use that work to create more electricity to sell, whereas W-in requires money to be spent (powering the machines providing work into the system).

In this case of an F1 turbo, W-out is not wanted for money; W-out is wanted to power the compressor as much as possible. We don’t desire a low amount of W-in to the system because we want to compress the air as much as possible.

Therefore, the aim of the turbo designers is to maximise both W-out and W-in to gain as much performance as possible. This means that the turbine and compressor need to be designed for 100% efficiency to prevent losses, but of course, there are turbo size restrictions that limit the maximum power the engineers can get out of the turbo.

The actual inclusion of the turbo into the power unit provides the largest efficiency increase. The exhaust gasses that would otherwise be wasted are now used to create work. That work created is used to power the compressor, which in turn provides better combustion for the ICE.

This has been a very basic example as it doesn’t include any hybrid features such as the MGU-H etc. I just wanted to demonstrate what efficiency actually is and how it can be increased by not wasting anything that still holds some energy, in this example it is the ICE waste gases running a turbocharger.

If you enjoyed this different take on the 2014 Power Unit please share it, or retweet it on Twitter. Don’t forget to follow @HybridAliF1. Thank you for reading!

Ali