Mercedes' use of various engine modes has become a talking point again in 2018 after Lewis Hamilton's dominant pole lap in Australia -- most of the focus has been around what the four-time world champion labelled the team's "party" setting ahead of the season.
The original V6 turbo engine introduced by Mercedes in 2014 -- and the various evolutions to it in the years since -- put the German marque top of the pecking order, where it has remained for the dominant spell it is currently enjoying. Although various factors are credited with that success, the team's incredible run of pole positions (between 2014 and 2017, it claimed 71 of the 79 available) has been crucial.
Hamilton secured another to start the 2018 campaign, taking pole at Albert Park by more than 0.6s after being closely matched with Ferrari in the first two qualifying sessions and on the first run in Q3. That led to speculation that Mercedes' 'party mode' -- the engine setting it reserves specifically for the Q3 shootout between the ten quickest qualifiers -- was a major factor. It has not been uncommon in the V6 turbo era for Mercedes to find a big step in performance between Q2 and Q3, although the team insists Hamilton was using the same setting throughout all his quick laps in Q2 and Q3 during the opening qualifying session of the year.
Team boss Toto Wolff downplayed the size of the gap, calling Hamilton's lap "an outlier", while Sebastian Vettel said Ferrari's GPS data proved the lap was more down to his rival's ability in the corners than the power of the engine on the straights. Red Bull boss Christian Horner was at the opposite end of the spectrum, suggesting Formula One should move to prevent teams making engine changes between the start of qualifying and the race -- although it should be noted that Renault does not have an 'party mode' of its own.
Ahead of the Bahrain Grand Prix, Mercedes has explained how its various engine modes work throughout a race weekend.
What are engine modes?
Engine longevity is more important than ever in 2018, with drivers limited to just three engines (and two of some components) for the entire 21-race season. That means teams this year are juggling reliability and performance more delicately than ever before. The settings of the engine, and how those various parts interact together during the various parts of a grand prix weekend, are therefore crucial.
As the team explains: "PU [power unit] modes are a combination of settings that adjust the performance of the ICE [internal combustion engine] as well as the flow of electrical energy. The ICE performance is changed, for example, by varying the amount of fuel that is injected into the combustion chamber or by changing the timing of the ignition.
"For the Hybrid side of the Power Unit, the modes will alter the interaction and scheduling of the electrical energy for both deployment of the 120kW (maximum) MGU-K and recovery of both the MGU-K and MGU-H."
Mercedes has confirmed it has three basic modes for any given grand prix weekend: one for the majority of free practice sessions, one for the majority of qualifying, and one for the majority of the race. In addition, "all three can be altered with various sub-settings for different situations, which control whether electrical energy is being net deployed over a lap, recovered or used in a balanced manner (with energy deployment and recovery balancing each other out)."
In other words, each mode available to the driver has various levels or degrees of performance within it.
How are these engine modes used?
Conservation is the name of the game in free practice, meaning it is unlikely Mercedes ever shows anything close to its one-lap pace during the qualifying simulations which tend to take place during second practice. Given the nature of the restrictive regulations, this mindset also trickles over to Sunday. The team's race strategy includes a "recovery energy management mode" as the team juggles the potential for "ballsy on-track passing and tactical strategy".
The higher performance settings are used earlier in the race, when the battles for track position are crucial, and around the pit-stop windows, before a more conservative approach is adopted. As Valtteri Bottas had done earlier in the race after hitting a train of traffic, Hamilton turned his race mode down in the latter stages of the Australian Grand Prix, having lost the lead to Vettel and realising passing on the Albert Park track was all but impossible.
All of these decisions are framed by the team's "phase document", which defines the absolute limit of the power unit at every race weekend based on the specifics of each circuit and the data collected in practice sessions. This information is the same for Mercedes' two factory cars and each customer team running one of its engines.
In the teams own words: "PU modes are defined when the first set of hardware is tested in Brixworth [its engine factory] and the mileage limit is determined by the success of the long-run programme. Some of these are circuit-specific, others are more general. Making the call on which mode to use can either be the driver's decision, or through the advice of the engineering team -- who will communicate over the radio which settings to adjust and which mode to switch to."
What is the 'party mode' and how does it work?
The second of the modes listed above has generated the most attention over the past few weeks. Mercedes has not denied it has extra power reserved for the final stages of qualifying, the main debate is around just how much of an extra advantage this mode gives the team.
The 'party mode' -- the phrase coined by Hamilton himself on the eve of the season -- is used sparingly and is only available for a few laps each weekend, with usage varying "according to the competitive context" of each qualifying session. Using the "phase document", Mercedes will also take into account circuit characteristics when arriving at a decision at how much power is required on any given Saturday.
Although a huge advantage for any team, this is deflating for Mercedes' rivals; Daniel Ricciardo likened Hamilton's impressive Melbourne pole lap to getting "a pie in the face". Mercedes signed off its engine mode explainer with a rather ominous reminder that F1 has not yet ventured to the sort of circuit it has traditionally excelled at since 2014, suggesting more deflating moments are in store for rival teams this year.
"PU modes are particularly significant at power-sensitive circuits such as Spa-Francorchamps or Monza, which are dominated by long straights and acceleration zones. The first power-sensitive track on the 2018 F1 calendar is Round 4 in Baku. It will be interesting to see how the storyline around engine modes develops as the season progresses, particularly when F1 reaches those more power-sensitive venues."