It was 2016 when Mahle revealed the principles behind the TJI Combustion System, an acronym for turbulent jet ignition, i.e. turbulent jet ignition. It was a solution developed specifically for Ferrari’s engines, which made a huge leap in performance, and partly bridged the technical gap from Mercedes units, powerful with a very similar concept since the dawn of the turbo-hybrid era. The finale of the last three races in Belgium, the Netherlands and Italy allows us to deepen the discourse regarding the 2026 engines, whose regulations remain quite ambiguous towards TJI-like combustion philosophies. Indeed, despite the increase in electric power, a large part of the research will focus on the heat engine, to make the most of the new alternative fuel concept. However, while some provisions of the Technical Regulations may appear unfavorable to immediate combustion strategies, others instead encourage this particular path.
Before getting into the folds of Regulation 2026, a step back is needed to delve into the TJI combustion. It stipulates that there is only one fuel injector per cylinder, a limit imposed by technical regulations that also prohibit indirect injection strategies. An insignificant part of the injected fuel, within 2-3% of the total charge, moves by the pressure gradient inside the primary combustion chamber, which is obtained through a “wall” built around the spark plug, giving life to the relatively rich local mixture, i.e. Relative abundance of gasoline compared to the air present. On the other hand, the combustion factor in the main chamber reaches a smaller volume composition, the amount of air predominating over gasoline, resulting in a particularly homogeneous mixture. The electric discharge from the candle ignites the rich mixture inside the preparation chamber, the explosion pushes jets of plasma into small holes along the median wall. Thus these jets spread radially within the main combustion chamber and their high temperature ignites the lean mixture in the cylinder. Compared to traditional combustion, where a single flame front from the candle in the middle spreads outward, In TJI, jets of different charge ignite at several points on the edge of the combustion chamber. This results in many flame fronts, able to spread out simultaneously and cover the entire cylinder volume in shorter times, reducing combustion times. This speed ensures that less heat is dispersed onto the walls, while it is possible to approximate more constant volume combustion, which is much more efficient than continuous pressure such as the normal Otto cycle pressure. Finally, the possibility of using a light mixture in the combustion chamber reduces the risk of detonation, This allows to increase the cylinder compression ratio With great advantages in terms of efficiency.
Full or partial spontaneous combustion, whether in the form of a TJI or in other deflections, ensures a significant increase in thermal efficiency so that, with the same fuel injected, this is limited by the regulation, releases a greater amount of energy. However, in 2026, the maximum compression ratio, a parameter that indicates how much the pistons put pressure on the combustion factor inside the cylinders, will move from the current value of 18 to 16. Claudio LombardiThe former director of Ferrari’s engine department emphasized how much this would penalize the benefits offered by combustion of this type and the possibility of creating more extreme strategies that work without the spark plug: As for the compression ratio being limited to 16, in my opinion it would not penalize the existing motors, but rather It will punish the development of engines known as compression ignition and homogeneous chargeimportant developments. The homogeneous charge provides the combustion generated by the spark plug, which automatically becomes beyond certain power levels and these are the developments that the various research centers focus on, because the efficiency increases dramatically. All of this, however, is associated with compression ratios in all likelihood higher than 16, which is why this research was banned. It’s kind of a contradiction, given that the introductory room is given in the regulation, in which there appears to be no restrictions on size or other aspects. So I’ve looked carefully at this in the regulations and even with a limited compression ratio, there doesn’t seem to be any limit to the size, shape, or number of holes in the pre-chamber.”
Thus it appears that the 2026 regulations discourage or at least limit the possibility of research into spontaneous ignition combustion. On the other hand, there is no shortage of other innovations in the new legislation which appears to encourage alternative strategies to traditional strategies. “The other limitation is the only injector made for all by the same supplier, with The only freedom regarding the injector holes itselfor one spark plug per cylinder, with coil supplied by FIA and maximum discharge energy of 80 mJ‘, always referring to Lombardy. The net standard injector is thus given freedom to develop the nozzle orifices, which are directly connected to the injected fuel mist, and to mix and transfer it to the various combustion chambers. On the other hand, The maximum pressure of the injection system will drop from the current 500 to the current 350 bar. However, the most significant change is related to the candle, as Article 5.12.1 marks an important turning point. While currently up to five discharges per cylinder are given per engine cycle, allowing greater control over the evolution of combustion from ignition to extinction, From 2026 it will be limited to one dump. On the other hand, the new regulation does not express the possibility of modulating the intensity of the discharge, thus simulating multiple ignition, but limits the total energy that can be discharged from each spark plug per cycle to 80 mJ.
So it is understood between injection pressure, compression ratio and use of spark plug The combustion management of the following engines will change dramatically. On the other hand, the increased economic use of the candle appears to be placing itself in a position of regulation that tends to rely more on alternative ignition dynamics, such as fully or partially spontaneous combustion. However, leaving the use of the candle free, would not have affected the exploitation of the introductory chamber, but, on the contrary, would have confirmed its benefits by increasing the accelerated combustion, as Lombardi always emphasized: “All of this limits research, even for the electrical part, as with the same coil for everyone, heat engine development is very limited. The more energy the candle provides, the faster the primary combustion nucleus will growwith advantages. Allowing the freedom to develop coils with such energy to make a multiple ignition discharge with significant energy is part of the research, but from 2026 it is limited as the maximum energy will be charged at 80 mJ. On the other hand, the real combustion is the initial combustion, which is actually a super candlebut high-powered lighting will also lead to advantages with the introductory room.”
Thus, the limited power of the spark plug is combined with the reduced fuel flow rate, and the restrictions on compression ratio and turbo pressure to limit the power of the thermal engine, in a way that compensates for the increase in the electric part. In general, it is difficult to understand in advance which combustion strategies will be applied in 2026, whether they are conventional or innovative and increasingly efficient. This is a ruling that will have to wait another four years.