1.21 Gigawatts?

Buckle in guys, here's the long promised article on LMP1 hybrid subclasses.  Sort of.  All four LMP1-H manufacturers have declared which hybrid subclass they will be running in this year, and official preseason testing is underway at Paul Ricard, meaning for the first time (that I'm aware of), we have some hard data that we  can judge the 2015 LMP1-H cars by.  For 2015 we have the full range of hybrid subclasses covered.  Nissan's car will run in the 2 megajoule class (the lowest hybrid subclass), Audi's car increases from 2MJ in 2014 to 4MJ for 2015, Toyota remains a 6MJ car, and Porsche increases from 6MJ to 8MJ, making it the first 8MJ car entered in WEC competition.

At this point your asking what the heck is all this megajoule stuff and why do I care?  I won't go into a ton of technical detail (this isn't Mulsanne's Corner, and I couldn't explain what a supercapacitor is if my life depended on it), but I do feel that a very basic understanding of the hybrid systems on these cars is important to understanding the strengths and weakness of the various machines.  Like I've said before, I'm not an automotive engineer, and I don't have any insider information, so this article might contain a few (or many) technical errors, but I do the best I can.

Okay, so what is the deal with these hybrid subclasses.  The FIA rulebook for the LMP1-H cars has four hybrid subclasses based on how much electric energy the car is allowed to use per lap to supplement the power produced by the internal combustion engine.  (In case any engineers are reading this, I know I know a Joule is technically a unit of work, not energy, but frankly I can't be bothered to care about unit consistency at the moment, so just deal with it).  The FIA rulebook contains equivalency rules that attempt to balance out the performance of the various subclasses.  Specifically, if your car is in a lower class (like Nissan and Audi), you are allowed a higher fuel flow per lap, meaning you should get more horsepower from the internal combustion engine, while the higher hybrid subclasses (Toyota and Porsche) are allowed to use more electric power, giving them a stronger boost out of the corners from the car's electric motors, but they have a lower fuel flow per lap.  What this means that in theory, each car is given the same amount of potential energy per lap either in the form of gasoline (or diesel if your Audi and insist on using the same basic engine you find in a Caterpillar D7 dozer) or stored electric energy.

In the world of the WEC though, some hybrid subclasses or more equivalent then others.  Just looking at car performance in 2014 for a second, it is easy to see that the 6MJ Porsche and Toyota performed better then the 2MJ Audi.  No one has ever confused me for being a mechanical engineer, but if we look at some general performance numbers for internal combustion engines and electric motors, you can see some basics reasons why a higher hybrid subclass (done properly) is a better design.  According to my technical sources (okay, I went to Wikipedia), internal combustion engines have a maximum theoretical efficiency of 25% to 30%.  This means that of the energy released by the burning fuel, only 25% to 30% of that energy actually moves the car forward.  Electric motors on the other hand have a theoretical efficiency of 100%, with a practical efficiency of around 90%.  Let's put that perspective for a second.  The real world efficiency of an electric motor is three times greater then the theoretical efficiency of an internal combustion engine.  Now let's logically think about how this applies to racecars.  Each car is (basically) allowed to use the same amount of energy per lap, but if more of the energy is electric, a greater percentage of that energy will be used for actually moving the car, instead of making heat and noise.

Thoroughly confused yet?  Yes?  Good.  At this point, you're also probably asking, who let me on the internet?  Good question.  You're also probably asking if the larger megajoule subclass cars are faster, why don't all the manufacturers just run in the 8MJ subclass?  Two reasons.  First, storing energy for an internal combustion engine is as simple as adding fuel to the tank, but to the teams can't add extra electricity to the cars during pit stops.  If they could, Formula E would be a lot more interesting.  Instead, teams have to recover waste energy over the course of the lap and store it as electric energy (think Toyota Prius on steroids).  The higher your subclass the more energy your recovery system needs to able to scavenge per lap.  It's easy to claim that you have an 8MJ car, but that's only true if your energy recovery system can scavenge 8MJ's worth of power.  If you declare your car into a subclass were you can't recover enough energy, not only are you not taking full benefit of the hybrid system, your internal combustion engine will be down on power compared to a car in a lower subclass using the same amount of electric power due to lower fuel flow number for the higher hybrid subclasses.

Assuming your head hasn't completely exploded yet (or you left to watch cat videos on Youtube), there's even more things for teams to think about.  All this equipment to scavenge and store the electric energy, plus drive the wheels, weighs a lot.  So, not only do you need to make sure that your hybrid system is efficient enough to generate the amount of electric energy needed for your subclass, you need to make sure that car isn't too heavy.  Kind of hard to go fast through the Mulsanne chicane when your effectively giving a baby elephant a piggy back ride.

I'm guessing that none of you are still reading at this point, and those that have are yelling at their computer at all the technical mistakes I've made.  To summarize though, performance of the 2014 LMP1-H cars suggest that the higher hybrid subclasses have a speed advantage, but only if the energy recovery system can scavenge enough electric energy, and do so without turning a svelte racecar into a porker.  Team's who can't overcome these two technical challenges are better of entering their car in a lower hybrid subclass.

I'm leaving out some of the fine details of the hybrid systems on these cars, but this article is too long as is, and I think I've hit the high points.  Tune in tomorrow for a trade mark Racing Nerd uninformed analysis of the 2015 WEC LMP1-H competitors.