KTM TPI, two-stroke injection: This is how it works!
In motorsport circles it was an open secret that KTM was working on an injection system for a two-stroke engine. We have to give it to the Austrians: They have become trendsetters and have drastically shaken the cards in the motorsport world. Before the turn of the century it was mainly the “Big Four” from the land of the rising sun who called the shots, but now things are somewhat different.
In Mattighofen, the R&D department is apparently running at full speed because no challenge is too much for them. Although injection on a two-stroke is not new, KTM had to make it "workable and manageable" on an enduro motorcycle. And that was apparently not easy because the engineers spent 15 years developing the system.
The launch was reported as big news in every trade magazine earlier this year. The first photos appeared as well as some videos of celebrities (read: Johnny Walker) from the enduro world who recommended the machine. You can tell from everything that KTM is very proud of the work it has done. The first independent tests were very positive. The guys at KTM wanted a characteristic two-stroke with the “carburettor feeling” but without the disadvantages. They certainly succeeded in that. What our test rider thinks of such a KTM TPI enduro found, you read here.
Euro4 standard as (extra) motivation
But why did KTM specifically want injection on their two-strokes? There are several reasons for this. First of all, there is the pressure of environmental legislation. Nowadays (since January 1, 2017) engines have to be Euro 4, but that was hardly feasible on a two-stroke for competition use which also has to be street legal. Furthermore, two-strokes are greedy with gasoline. It is typical for these types of engines to spill quite a bit of gasoline. Part of the drawn-in gasoline is not actually converted into power and may be considered wasted. So a two-stroke could be a bit more economical.
If a two-stroke is equipped with injection, this naturally also includes some electronics. To change the characteristics of the engine in a conventional “smoker”, you had to work with nozzles and needles. You did this, for example, because the circuit deemed it necessary, the air pressure had changed due to driving at a high altitude or when the weather conditions required it. With an injection-based version you do this by changing the mapping. So you change the injection by choosing a different type of mapping.
And then there is also the timing of the release of this technology. The FIM has decided to change the rules surrounding the European Motocross Championship from this year. Since the advent of four-strokes, a 125cc two-stroke was the equivalent of a 250cc four-stroke. This rule now changes as follows: 125cc is 125cc, four-stroke or two-stroke. It is suspected that the FIM also wants to apply this in the MXGP and MX2 next year. If that is the case, then KTM is set with their timing because it goes without saying that they will also introduce this great technology to motocross. Perhaps KTM will use some extra time to give the two-stroke injection the specific character of a dirt bike.
How does KTM's two-stroke injection system work?
The principle of a two-stroke is of course retained. The flushing ports on the side of the cylinder continue to function as passage channels. KTM also calls it TPI or Transfer Port Injection. However, this time it is only sucked in air and not a freshly made mixture from a carburetor. The Dell'Orto throttle body only serves to regulate the amount of air sucked in. So there is no injector in the throttle body as with the four-stroke injection engines. There is a cold start system on the house that adds extra air via a by-pass. KTM has screwed an injector into the two flush channels on the side of the cylinder. Gasoline is pumped under pressure from the fuel tank to the injectors, which then open and close on command from the ECU or on-board computer. The injectors inject downwards and thus ensure perfect mixing of the sucked air that enters through the throttle body. The ECU (KTM calls it EMS or Engine Management System) takes into account the story told by a number of sensors. These provide information about the pressure of the sucked air, the barometric pressure, the position of the throttle lever, the speed and the temperature of the cooling water and oil. With these parameters, the on-board computer makes millions of calculations per second to always inject the correct amount of fuel. The injected engines are equipped with a high-performance power system so that the ECU and fuel pump always receive sufficient voltage. The engines that were previously equipped with carburetors did not require so much electricity, that's why.
Bye, bye premix
Two-stroke engines work as usual with a mixture of gasoline and oil to lubricate the intestines. By innards we mean the piston, the cylinder, the big end and the crankshaft bearings. Premixing is no longer necessary with these ultra-modern KTMs: The engines are equipped with a separate 0,7 liter oil tank. This would in principle allow you to empty six to seven petrol tanks. Both the petrol and oil tanks have an indicator light on the dashboard. The oil tank filler cap is located just behind the steering head. So the oil is also injected into the system in a controlled manner just after the throttle valve. In concrete terms, this means that the KTMs run on variable mixture lubrication. In other words, the computer determines the required amount of oil. The mixing ratio varies between 1:60 and 1:100. You no longer see these Austrians smoking, only the smell remains. Conventional two-strokes often filled up and had to be burned clean by holding the throttle open to the ridge for a while. This is already a thing of the past: Thanks to the fuel injection, which is always precisely regulated, the engine always has the right amount of petrol (and oil) available. The engine continues to idle smoothly, even if it falls over. The consumption of the injected KTMs would also approach that of the current four-strokes and that is very impressive. This way, your four-stroke buddies won't look down on you the next time you're waving that you urgently need to go to a gas station.
The introduction of injection has lost some of the simplicity of a two-stroke, but its advantages are undeniably great. With this step, KTM takes a significant lead over their competitors. They will undoubtedly have to follow because the revival of the two-stroke is now unstoppable! You can learn more about the revolutionary TPI technology here proofread.
Tekst: Danny Hermans
Photos: KTM
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