Anti-lag on a diesel - possible?

[mat777]

I know that petrol anti-lag turbo systems squirt a glob of fuel into the exhaust between manifold and turbo when you lift off the throttle, causing the fuel to combust and keep the turbo spun up. I was pondering with a friend the other day whether or not this would be possible with a diesel though, due to the higher combustion temperature of diesel meaning it would likely just make a nice cloud of smoke like a skywriting plane.

Does anyone know whether it would work? Just a hypothetical idea borne out by turbo lag on my TD5, unfortunately I know they are illegal on the road

[Kozy]

Diesel ignites under pressure, there isn't enough on the exhaust stroke to do that, so I'm going to go with no.

[beanbag]

Kozy said:

Diesel ignites under pressure, there isn't enough on the exhaust stroke to do that, so I'm going to go with no.

Have a separate petrol and diesel tank!

[Monkeylegend]

The variable vane turbo eliminates lag, well it does on my diesel.

[Kozy]

beanbag said:

Have a separate petrol and diesel tank!

Injector and spark plug just before the inlet housing, turn it into a jet turbine! It would be fun for the 500m the turbine lasted...

[TheEnd]

That's the same TDS engine they used in the BMWs and Omegas? If that's the case, get a chip for it and Bob will then be an Uncle.

[Mr2Mike]

Anti-lag systems typically do not inject fuel directly into the exhaust manifold. Instead the fuel comes from the normal fuel injector and the air either comes from keeping the throttle slightly open, or from air injected directly into the exhaust manifold. You could retard the injection point in a diesel I suppose, but since a diesel it not usually throttled (some are though) you'd be getting full boost into the cylinder whilst ALS was active.

Monkeylegend said:

The variable vane turbo eliminates lag, well it does on my diesel.

No it doesn't, you are confusing boost threshold (which is what VNG improves) with lag.

[rhinochopig]

Lots of ways it *could* be done. Electrically assisted spool. Accumulator that charges on full boost and release when below boost threshold or keeps the Tubby spooling. The question though is why you'd want to. VVG does a good enough job, and...well...it's a diesel so does it doesn't matter that power isn't delivered in a N/A fashion.

[Monkeylegend]

Mr2Mike said:

Anti-lag systems typically do not inject fuel directly into the exhaust manifold. Instead the fuel comes from the normal fuel injector and the air either comes from keeping the throttle slightly open, or from air injected directly into the exhaust manifold. You could retard the injection point in a diesel I suppose, but since a diesel it not usually throttled (some are though) you'd be getting full boost into the cylinder whilst ALS was active.

Monkeylegend said:

The variable vane turbo eliminates lag, well it does on my diesel.

No it doesn't, you are confusing boost threshold (which is what VNG improves) with lag.

Well as it was explained to me was turbo boost is available at tickover hence no lag while the turbo spools up. I stand to be corrected however. I do know that my car doesn't suffer from turbo lag at any rpm.

[robmlufc]

VG turbos give you the benefits of small and large turbos, you will get less lag with VG as the turbo spins up quicker.

[rhinochopig]

Monkeylegend said:

Mr2Mike said:

Anti-lag systems typically do not inject fuel directly into the exhaust manifold. Instead the fuel comes from the normal fuel injector and the air either comes from keeping the throttle slightly open, or from air injected directly into the exhaust manifold. You could retard the injection point in a diesel I suppose, but since a diesel it not usually throttled (some are though) you'd be getting full boost into the cylinder whilst ALS was active.

Monkeylegend said:

The variable vane turbo eliminates lag, well it does on my diesel.

No it doesn't, you are confusing boost threshold (which is what VNG improves) with lag.

Well as it was explained to me was turbo boost is available at tickover hence no lag while the turbo spools up. I stand to be corrected however. I do know that my car doesn't suffer from turbo lag at any rpm.

That's still boost threshold. Lag is essentially the time taken for a turbo to spool back up to operating RPM after the throttle has been closed and then re-applied. i.e. when changing gear, lifting off, etc. Threshold is the point at which the turbo makes usable boost. Similar but different.

[Monkeylegend]

rhinochopig said:

Monkeylegend said:

Mr2Mike said:

Anti-lag systems typically do not inject fuel directly into the exhaust manifold. Instead the fuel comes from the normal fuel injector and the air either comes from keeping the throttle slightly open, or from air injected directly into the exhaust manifold. You could retard the injection point in a diesel I suppose, but since a diesel it not usually throttled (some are though) you'd be getting full boost into the cylinder whilst ALS was active.

Monkeylegend said:

The variable vane turbo eliminates lag, well it does on my diesel.

No it doesn't, you are confusing boost threshold (which is what VNG improves) with lag.

Well as it was explained to me was turbo boost is available at tickover hence no lag while the turbo spools up. I stand to be corrected however. I do know that my car doesn't suffer from turbo lag at any rpm.

That's still boost threshold. Lag is essentially the time taken for a turbo to spool back up to operating RPM after the throttle has been closed and then re-applied. i.e. when changing gear, lifting off, etc. Threshold is the point at which the turbo makes usable boost. Similar but different.

I am happy to stand corrected

[Megaflow]

If my understanding of anti-lag is correct, then no it can't be done.

As I understand it anti-lag works by keeping the fuel flowing when the throttles have been shut, but then putting a massive retard value on the ignition so it fires with the exhuast valves open. This keeps the exhaust gas spinning the turbo, but producing very little power as the exhaust valve is open.

If that is correct, then it can't be done on a diesel as diesel is compression ignition and the diesel won't ignite with the exhaust valve open.

[rhinochopig]

Megaflow said:

If my understanding of anti-lag is correct, then no it can't be done.

As I understand it anti-lag works by keeping the fuel flowing when the throttles have been shut, but then putting a massive retard value on the ignition so it fires with the exhuast valves open. This keeps the exhaust gas spinning the turbo, but producing very little power as the exhaust valve is open.

If that is correct, then it can't be done on a diesel as diesel is compression ignition and the diesel won't ignite with the exhaust valve open.

Depends on how you spool the turbo though. You can spool them via non exhaust gas means.

[Megaflow]

Very true. Electrically assited turbo's are very close to a production reality, however I'm not sure I'd class that as anti lag in the same sense as the OP is talking about.

[Mr2Mike]

Megaflow said:

If my understanding of anti-lag is correct, then no it can't be done.

As I understand it anti-lag works by keeping the fuel flowing when the throttles have been shut, but then putting a massive retard value on the ignition so it fires with the exhuast valves open. This keeps the exhaust gas spinning the turbo, but producing very little power as the exhaust valve is open.

If that is correct, then it can't be done on a diesel as diesel is compression ignition and the diesel won't ignite with the exhaust valve open.

The exhaust valve isn't open when it fires (you'd need some form of decompressor to achieve this), the ignition point is simply very retarded so relatively minimal pressure is built up within the cylinder before the exhaust valve is opened at the normal point by the camshaft.

[mat777]

Thanks for all the replies everyone. I wasnt seriously looking to anti-lag the car, I was just wondering if it was hypothetically possible on a diesel