Turbulent Jet Ignition: The next stage in GT500 engine development

Since its introduction in 2014, the Nippon Race Engine (NRE) formula, the two-litre, turbocharged, four-cylinder engines that power every car in the Autobacs Super GT Series’ GT500 class, have been a roaring success – reliable, efficient, and powerful beyond comprehension.

This generation of GT500 cars is already the fastest in Super GT history, thanks in large part to the new engine formula, combined with the ever-escalating tyre war between Bridgestone, Michelin, Yokohama, and Dunlop.

But believe it or not, a new breakthrough in the engine development battle between Honda, Nissan, and Toyota could result in even more record-breaking performances and higher speeds from the fastest GT race cars on earth: The introduction of Turbulent Jet Injection, or TJI, which was a breakthrough in Formula 1 engine technology in 2014 – and has now made its way into GT500.

F1’s 1.6 litre, 6-cylinder hybrid-turbo engine formula works within similar constraints to GT500’s NRE formula, with F1’s engines limited by fuel load, fuel flow, and turbo boost pressure limits for the sake of efficiency. It resulted in engine builders being challenged to find new ways to create more horsepower with the given constraints.

That breakthrough came from Mercedes-Benz in 2014, when they launched a new power unit with TJI combustion. By effectively replacing the traditional spark plug with a pre-chamber that ignites an ultra-rich reserve of fuel within the cylinder’s lean mixture of fuel and air, the combustion efficiency within the engine is improved dramatically, requiring less fuel to create a “spark” within the cylinder.

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© Mahle

In the absolute layperson’s terms, Turbulent Jet Ignition, or “Pre-Chamber” Ignition, allows for the same amount of power with less fuel burn as a traditional internal combustion engine. That efficiency can be expressed in the form of additional fuel economy, or additional horsepower.

It’s one of the many reasons why Mercedes have dominated Formula 1’s current hybrid era from 2014 to 2017. TJI was later brought in by Ferrari in 2015, then by the time Renault and Honda introduced it into their power units in 2016 and 2017, TJI was now universally seen as the new “breakthrough” in F1 engine building.

There are many fascinating and detailed reads on the subject as applied to Formula 1, such as this 2016 article in Racecar Engineering from NISMO TV’s Super GT commentator, Sam Collins. Or this article in Motor Sport Magazine from Mark Hughes. Or this primer from Mark Magda of EngineLabs.

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For Super GT, however, there is a great advantage for using TJI to increase combustion efficiency – as all teams are required to use commercial-grade petrol in their engines, made available at each circuit, as opposed to Formula 1 where teams can craft their own fuel blends within the set regulations and use them at any circuit.

This breakthrough in horsepower and efficiency is said to be a major factor in Super GT’s decision to tighten up its three-stage Success Ballast fuel flow restrictor system for 2018.

While Honda struggled for pace and reliability in Formula 1 for much of the last three seasons, they were still able to apply the TJI technology that they’d applied in F1 to Super GT mid-way through the 2017 season with an engine update. Not long after, Honda ended a long winless drought in GT500 with back-to-back victories in the Fuji GT 300km Race, and at the Suzuka 1000km.

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Lexus have also introduced the same TJI technology in their engines starting in 2018. Their strengths came from the package they started with in 2017, their advantages coming in the engine updates introduced at the end of 2016, plus the aero advantages that the LC500 had over the rival GT-Rs and NSXes.

Nissan have also adopted similar technology in their engines, but done so in a different fashion – they’ve integrated a traditional spark plug into the pre-ignition chamber.

All in all, Turbulent Jet Ignition is making one of the greatest modern engine formulas in racing even better, and in the context of the 2018 season to come, fans can expect several new lap records, and more importantly, the possibility of a shake-up in the championship battle in Super GT’s premier category.

Feature image credit: © Takashi Ogasawara / AUTOSPORTweb

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