Tech download: Tricks of the trade in IndyCar fuel saving

Gavin Baker/Motorsport Images

Tech download: Tricks of the trade in IndyCar fuel saving

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Tech download: Tricks of the trade in IndyCar fuel saving

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After discussing why teams will resort to fuel saving in the last column, the natural follow-up question is, how do teams go about doing this? While there are many strategic reasons that teams will turn to fuel saving during a race, in every scenario teams will try to save fuel in the most efficient way possible. That is, minimizing the lap time penalty as best they can while still hitting the fuel target.

How teams go about minimizing their lap time loss when needing to save fuel depends on several factors: the capability of the engine manufacturer to run different engine modes, the ability of the driver to adapt their driving technique, as well as the characteristics of the track and the current traffic situation. Engine manufacturers, teams, and drivers will work together and spend huge amounts of resources to optimize this aspect of performance, be it on the dyno, in simulation, or during track testing. The ability to save fuel without losing much time can be a huge differentiator throughout a race.

There are two primary techniques for saving fuel: the driver can either change engine modes, or incorporate lifting and coasting. Each has their own advantages and disadvantages, but they effectively achieve the same thing: completing the lap while saving fuel compared to running at 100%. Deciding the most efficient way to use one or both of these techniques over an entire lap however, is very difficult. Oftentimes, there are an infinite number of ways to hit the same fuel target, so teams will set about using the engineering tools at their disposal to find the best approach.

Engine modes

Changing engine modes is relatively straightforward. The engine manufacturer can load various settings into the car’s ECU, which can then be selected by the driver by adjusting a dial on the steering wheel during the race. Doing so will effectively (and without giving too much away) reduce engine power and fuel consumption in lockstep.

When it comes to fuel saving, this is where the battle between manufacturers lies. Offering reduced fuel consumption for the same power compared to the competition not only gives teams additional race pace when hitting the same fuel target, but also opens up the number of strategy options available to them.

Since fuel targets can change throughout the race, teams will always ensure there are multiple options available on the dial, each with its own compromise of power reduction and reduced fuel consumption. Teams will also use data from practice sessions to advise over the radio as to what engine mode should be used for a given fuel target. With engine modes, the driver can continue to push with their driving style while still saving fuel. Typically, when resorting to changing engine modes, acceleration is the biggest compromise to performance (though there is also an effect on top speed) due to having less power available. On the plus side, drivers can continue to attack brake zones and corner entries and they normally would.

Lift and coast

The most common fuel saving technique for a driver is ‘lift and coast.’ As the driver is nearing the end of a straight and approaching a brake zone, they will lift well before the normal braking point, coast without any input on throttle or brake for some distance, and then apply the brake when sufficiently close to corner entry.

Alexander Rossi showed just how effective the lift and coast approach can be at Indy in 2016. F. Peirce Williams/Motorsport Images

The idea is that fuel consumption is closely tied to being on-throttle, so if a driver needs to reduce consumption, they will have to lift for some amount of time during the lap. Lifting towards the end of a straight is ideal because this is when the driver is closest to top speed, so they will coast farther, and therefore save more fuel. Additionally, a car is accelerating much less at the end of the straight than it is at the beginning (since acceleration begins to taper off the closer the car gets to top speed), so lifting at the end of the straight is also less penalizing on lap time. Therefore, the higher the entry speed into a corner, the better it typically is to use lift and coast to save fuel.

The main benefit to lift and coast is that there is no de-tuning of the engine: acceleration for most of the straight remains the same as it would when not saving fuel. However, the detriment to lift and coast is quite clear: all the time loss is concentrated at corner entries.

Comparing fuel save methods

To get an initial comparison between approaches, engineers will turn to a vital tool called lap time simulation. This is a software that will use a numerically modeled car, track, and driver to solve physics equations as a way of creating data for a virtual lap as if it really happened on track, but with the benefit of every single parameter being controlled by the engineer.

Lap time simulation is a hugely complex subject in its own right; one that can do everything from investigating potential setups to predicting the effect of changing ambient conditions. It is one of the most important pieces of software an engineer will use. For the scope of this article though, it allows the engineer to compare fuel saving approaches to see whether changing engine mode or lift and coast is the fastest way to hit a fuel target.

Starting with the most basic of examples, a simulation of accelerating from the apex of one corner, down a straight, to the apex of the next corner is modeled. Running at 100% burns 0.301 gallons, but say the fuel target is 0.286 gallons (5% savings). The engine manufacturer – who has been doing some work on the dyno – says that they have three engine modes to try. The first is full power and full consumption (Mode 1), the next offers 4% power reduction for a 5% savings in fuel consumption (Mode 2), and the final option offers 8% power reduction for 9% fuel savings (Mode 3). Lap time simulation can be run iteratively in order to solve for the required lift and coast distance until the fuel target is achieved. Mode 1 is going to require 135 ft of lift and coast to hit the fuel target, Mode 2 will still need 50 ft of lift and coast, and Mode 3 can be run without any driving adjustments needed to be made. With these simulations, overlays of speed, fuel consumption, and lap time (plotted versus distance) can be compared to a push lap with no fuel saving, and the results can then be analyzed.

Move your cursor over the graphs to reveal additional details

In this example, all three fuel saving approaches use the same amount of fuel, but using Mode 1 and 135 ft of lift and coast is 0.23s faster than going straight to Mode 3. That is a massive amount of time for just one corner! Also of note, using Mode 1 and 135 ft of lift and coast is only 0.02s than pushing flat-out, which is hardly any loss time at all for using 5% less fuel. When done efficiently, the lap time loss from fuel saving can close to nothing.

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