How Do Formula 1 Power Units Work?

The basic process of an engine and the one that’s used for Formula One and most road cars is the four-stroke cycle. What are those four-strokes? And how do they happen? With the crankshaft, there is an axis of rotation. And then there is the offset crank pin. We connect from that offset crank pin from our con rods to the piston. And the stroke is when the piston moves from the top of the cylinder to the bottom of the cylinder or from the bottom to the top. A four-stroke cycle is one movement down, up, down, and up. And that corresponds to two rotations of the crankshaft.

There is the induction stroke, the compression stroke, the power stroke, and the exhaust stroke, or as they’re more affectionately known, suck, squeeze, bang, blow.

Let’s start with the induction stroke. With the piston at the top of the cylinder, it starts to move down, unit valves open, and it moves to the bottom of the cylinder. That’s the first stroke. In this phase the pressure inside the cylinder is slightly reduced as the piston moves down and the air ready for combustion then rushes in because of the pressure difference between the cylinder and itself. Also during that stroke the fuel gets injected directly into the cylinder. At the bottom of that stroke is a nice air fuel mixture.

In the second stroke there is a volume of fuel and air that gets compressed. The pressure goes up, the temperature goes up, everything’s ready and it’s just waiting to combust. And then nearing the top, the spark plug sparks and we get a combustion event so the prepared air fuel mixture will then combust and you get the power stroke.

In the power stroke the piston is then driven to the bottom of the stroke and that’s where via the con rods and that offset crankshaft, you then get a torque applied to the crankshaft. That’s where the power is coming from. Then the exhausts open, the piston moves up again, and excess fuel gets expelled through the exhaust pipe.

The combustion loads from the controlled explosion put a huge amount of pressure on the power unit. The pressure wave that forces the piston down is the equivalent of having four elephants sat on top of the piston. The temperatures are approximately 2,750 degrees C, which is half the temperature of the surface of the sun.

These combustion events all happen so fast, around 200 times in the blink of an eye.

If you multiply that for a qualifying lap, there are 50,000 combustion events in the engine happening over the course of one qualifying lap. That means 50,000 times the four elephants will sit on top of the pistons and the temperatures half of that of the sun will all happen within the F1 power unit.

There are a lot of similarities, as both will have a crankshaft, a rod, and a piston in every internal combustion engine. However, the design is very different.

The calculations that have gone into understanding how to transfer those four elephants from the top of the pistons to the crankshaft, and the level of detail and materials used in the construction, are worlds apart.

While the fundamentals are the same, it’s the details and the innovation put into the F1 power unit that makes the difference. Having said that, Mercedes recently announced they will use FORMULA 1 technology in the future production of their Mercedes-AMG supercars.

Force times distance equals torque. If you have a spanner on a nut, and you’re tightening that nut, you’ve got the force, which is you’re putting on the force, and then you’ve got the distance between you and the nut.

It’s the same thing in the crankshaft. You have the offset pin, you’ve got the rod coming down, so it’s a force offset. Therefore, you’ve got the force and the distance and that creates the torque on the crankshaft.

Horsepower, on the other hand, is very closely related to torque, but it’s the amount of torque you can have per unit time. So torque is the work done. Power is the work done per unit time. So if you think of a car that’s coming from a low speed, corner exit, trying to get to the start of the next corner, torque will be the amount of work done to get it to the next corner. Power is then when you start talking about time and with more power, the quicker you can get to that next corner, because it’s work per unit time.

Power relative to the RPM isn’t a straight line, it’s a curve. There’s a peak power somewhere around 10,500-11,000. What a driver really wants to do is get as close to that peak power and use as much of that power as possible with their gear changes.

The intention of a Formula 1 gearbox is to keep the engine operating right in its area of peak power, which won’t be right up at 15,000.

There is a regulation that allows the RPM to go up linearly, so it goes up in fuel flow, and then flattens out at 10,500RPM.

Below 10,5000RPM the car starts getting influenced by friction. With friction and the amount of force and rubbing lost through bearings, that goes up with speed and some parts being squared, so that all of a sudden the friction is getting much, much higher. And so that means that after that, you start to dip off and roll off the power. So it’s that shape of the power curve that’s being matched by the shift point.

De-rating means deliberately turning off the MGU-K, which is deliberately turning off 120 kilowatts of additional boost that the driver can get from that electric motor. This is done at the end of strokes, and is what the driver is feeling when they suddenly lose power.

The reason teams do this is because there is only a certain amount of energy that can be deployed either in some circuits that has a regulation based limit and other circuits, it might just be a layout based limit.

Basically there is a certain amount of energy you can use and teams have to choose where to use that energy.

The strategy mode (although banned since midway through the 2020 Formula 1 season) is a very simple switch for the driver to get to.

Teams collate a number of settings and put those on the strategy switch qualifying mode, and use the engine in different ways for different strategies.

The HPP mode is the next level down where teams change some of those settings within the collection to get it to do exactly what they want. Typically, if a team is changing the HPP mode, it means they’ve got something a bit wrong at the factory ahead of the race, and need to change it.

Simply put, thermal efficiency is the ratio of the amount of power that’s coming out to the potential power that you put in with the fuel.

If you take the amount of energy that is tied up in the fuel and the rate that that fuel is being supplied to the engine, you’ve got a certain amount of energy. And if you think of it that’s power by using time, you’ve got a certain amount of power that’s possible to release from the fuel, which teams can measure.

For example, Petrobras measure the power released from their fuel so McLaren knows exactly how much energy is available. They then burn that fuel in the four-stroke cycle. They then measure how much power they are getting out.

Thermal efficiency is even more important on a road car, as it means less waste and less fuel used for consumers.

In Formula 1, the regulations say you can only use a certain amount of fuel per second. So if a teams thermal efficiency is higher, they are getting more power out of that certain constrained amount of fuel, and will be creating more power than your competitors.

Engine knock is when you have an uncontrolled combustion event.

To understand what engine knock is, we need to go back to the four-stroke cycle mentioned earlier, when you have that compression stroke of the fuel and air.

As we get to top dead center on that compression stroke, we spark the spark plug and you get a small flame kernel. And then that small flame kernel very quickly expands, burning all the fuel air mixture. And it does that in a beautifully controlled way.

What happens with engine knock is during that compression stroke, as you get to the top, if the team haven’t had the mixture preparation right there is a physical hotspot on the piston or cylinder head.

It might get to a point where that very, very local pressure and temperature means that before the flame actually gets there, there is an uncontrolled combustion event where you have a very local detonation, and that causes an incredible shock wave that then goes through the cylinder.

Engine knock can erode the pistons, and the amount of force that then puts through the whole system can be catastrophic.

A trend that first started with road cars and moved into Formula One as well is where you turbocharge an engine rather than making it naturally aspirated, which allows manufacturers to downsize.

When we were talking about the four-stroke cycle and we were talking about when the piston in the induction stroke created a Delta-P in the cylinder, which then meant that the air could come in, if you’re turbocharging it, you’re increasing the pressure at the point of entry so that you were ramming in as much air as you possibly can, which allows you to put more fuel in which therefore means that you’re getting the same amount of force through the crankshaft and the same amount of torque through the crankshaft as if you had more cylinders, but was naturally aspirated. It is this real skill of reducing the size, but making the bang the same that engine manufacturers need to get right.