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Anti-Lag on Direct Injection

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I'm interessted to hear if there are any specific strategies for Antilag on DI engines?

For example can fuel be injected into the exhaust stroke, so combustion happens in the exhaust manifold?

What risk are involved to do that? For example could "pre-ignition happen on exhaust stroke?

Hi Adrian, I haven't really had much to do with antilag tuning on DI engines so I don't claim to be an expert on this particular topic. Obviously DI gives you more freedom around the introduction of the fuel and on face value yes, you could inject fuel on the exhaust stroke so it's going straight out the exhaust. The issue I'd see with doing this however is that we still actually need combustion occurring within the engine to keep the engine running in over run conditions. If you were to inject the fuel during the exhaust stroke this would do a great job of getting the fuel and air into the exhaust system, however that alone won't provide any torque to keep the engine operating since there would be no fuel to support even late combustion during the power stroke.

Ultimately you'd need to experiment to see how this actually plays out but on face value I don't think it would achieve the aim.

Hi Andre

Thank you for your answer, which leadet to my next questions.

Suring overun the air and fuel will ignite pn tje glowing exhaust manifold. During overun drivers usually don't want the engine active pushing (at leat the Pro driver I worked with)

But yes if ignition retard should be applied also on low part throttle to help build boost, then it is not possible to inject into exhaust stroke. Except if the ECU-Engine combination allows lean burn and split injection.

So what I'm wondering how is a antilag usually setup on Rally cars or GT3? Is ign retardet up to lets say 20% Acceleration Pedal position, throttle more opened, but ign retardet to keep engine torque on the same level as with Antilag off?

Are there certain strategies which produce less heat for the same boost level? So what better more ign retard or more cut resp which combination?

Hi Andre

Thank you for your answer, which leadet to my next questions.

During overun the air and fuel will ignite on the glowing exhaust manifold. During overun drivers usually don't want the engine active pushing (at leat the Pro driver I worked with). Means zero torque is wanted. Engine breaking can be controlled based on RPM and pre throttle boost.

But yes if ignition retard should be applied also on low part throttle range to help build boost, then it is not possible to inject into exhaust stroke. Except if the ECU-Engine combination allows lean burn and split injection.

So what I'm wondering how is a antilag usually setup on factory Rally cars or GT3? Is ign retarded up to lets say 20% Acceleration Pedal position, throttle more opened, but ign retardet to keep engine torque on the same level as with Antilag off? Or is it reallx only active during overun condition?

Are there certain strategies which produce less heat for the same boost level? So what is better, more ign retard or more cut resp.which combination?

My experience of what is being done on high end race/rally cars with DI anti lag is that they are randomly cutting fuel/retarding spark and advancing the cam to get a greater amount of overlap. This allows the excess boost to be passed through the engine without extra fuel being supplied (similar to the Cold/Hot blowing of the diffusers that F1 used a few years ago) so that they have a more progressive anti lag operation and it doesn't abuse the valve seats/springs as much. They still have enough mass flow through the engine to maintain the boost levels that they are after, but it also doesn't "push on" as much, meaning that the drivers have more control under braking.

This assumes that they are also running DBW.

Some ECUs simply inject on the exhaust stroke on a few of the cylinders and the remaining cylinders will have injection as normal to keep the engine running... This also goes for ignition... Eg. 1 & 4 cylinders will have ALS strategy enabled on an engine cycle, and 2 & 3 cylinders will run as normal to keep the engine running. The next engine cycle they would swap so the cylinder pairings would alternate roles. This is why you hear on some cars that low misfiring grunt off throttle when the ALS is active.

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