F1 Tech: What Is Turbulent Jet Ignition?

Mercedes reportedly built its turbo V6 under the new rules with some form of Turbulent Jet Ignition.

Turbulent Jet Ignition in Formula 1 race engines?

It sounds futuristic if not contrived. Almost like Transplasma Fusion Injectors or VTEC Cross-drilled Halogen Fluid.

Spark plug design has been rather consistent since the automobile was invented. However, new technologies such as Federal Mogul’s ACIS uses high-frequency electrical fields to create streams of ions that ignite the fuel mixture. Microwave, plasma and lasers have all been studied as replacements for the traditional spark plug.

But TJI is the hottest buzzword on the F1 circuit right now after numerous media outlets reported that Mercedes has been utilizing a form of this technology since the turbo V6 era arrived a couple years ago. Ferrari then adapted the technology last year, and it’s reported that Renault will join the party shortly, possibly at the Canadian Grand Prix.

Improving combustion efficiency is key for F1 engineers since the regulations limit the total amount of fuel that can be used in a race as well as the fuel-flow rate. This new technology replaces the standard spark plug in each cylinder with a jet ignition chamber and helps support ultra lean-burn operation in gas engines. If properly designed, this jet igniter can be a drop-in replacement for the spark plug.

It’s basically the most advanced evolution of ignition since the basic spark plug was invented over a century ago. There have been plenty of alternative spark technologies proposed over the past few decades by engineers, including using microwave, plasma and even lasers to ignite the air-fuel mixture in an internal combustion engine (ICE). But Formula 1 doesn’t allow any type of high-frequency ignition, and automakers have yet to find an alternative that’s as cost-effective as the traditional spark plug.

Illustrations from Mahle found on the internet show a TJI system designed for production engines that features two injectors: one in the port for the main charge and one to supply the ignition chamber.

Another view of the TJI system.

At first, observers surmised that F1 engine builders had solved all the mysteries and problems of homogeneous charge compression igntion (HCCI), or at least were using a form of HCCI along with spark ignition. HCCI is somewhat the holy grail of combustion for an ICE, since it theoretically leverages the best benefits of both spark and compression engines. In its simplest form, an HCCI engine draws an air-fuel mixture into the cylinder, similar to a gas spark engine, then then ignites the mixture using compression, similar to a diesel engine.

There is no spark or fuel-delivery timing, but there’s a much lower temperature combustion. That means lower NOx emissions and higher heat efficiency, which cuts down on CO2 emissions. The only problem is that there are no timing controls. Ignition is solely at the mercy of the laws of chemistry and physics, so high-speed and high-load conditions where cylinder temperatures rise can be a quite unpredictable.

You can see why a frenzy spread through the F1 discussion groups and media. But most recently it was revealed that TJI was the technology in question. When the secret spread to Ferrari, the Italians had a great partner in Mahle, an aftermarket supplier that has been touting the benefits of TJI since the turn of the decade.

As mentioned earlier, TJI replaces the spark plug with a jet ignition chamber. During the compression stroke, around 97 percent of the fuel charge is injected directly into the cylinder and the remaining three percent of fuel is directed into the chamber where a traditional spark plug ignites that small, overly rich charge within the tiny confines of the chamber. The resulting high-pressure jet stream of hot gasses are forced through a number of tiny holes in the chamber and into the main cylinder to ignite the rest of the air-fuel charge, which is by now thoroughly mixed and lean. According to Mahle, these hot jets fire out to the edge of the piston to ignite the mixture.

Here’s a closeup of how the Mahle TJI component would be in a production engine.

From a Mahle annual report: “While ignition normally takes place in the center of the cylinder, with Mahle Jet Ignition it essentially takes place from the outside toward the inside. This allows significantly better combustion of the fuel mixture. The result: more power with considerably less residue.”

When word of TJI first broke, many publications used illustrations from early Mahle reports and presentations, but the equipment depicted was for a production engine that utilized two injectors per cylinder: one for the main air-fuel charge and a secondary injector just for the ignition chamber. However, Formula 1 allows only a single injector per cylinder, so team engineers had to design a unique combustion chamber with a pre-ignition chamber that supports the spark plug, yet can still draw that 3 percent of fuel from the injector. The final effect is still the same with flame jets coming out of the small chamber and igniting the compressed air-fuel mixture at several points simultaneously in the cylinder.

Depending on the size and number of holes in the small ignition chamber, the flame jets can be manipulated to ignite the fuel simultaneously in different areas of the cylinder.

About the author

Mike Magda

Mike Magda is a veteran automotive writer with credits in publications such as Racecar Engineering, Hot Rod, Engine Technology International, Motor Trend, Automobile, Automotive Testing Technology and Professional Motorsport World. He was the editor of four national automotive magazines, including Chevy High Performance, and has authored hundreds of automotive technical briefings. In covering nearly every type of motorsport, Mike has collaborated with many of racing's top engine builders and factory engineers.
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