Questions about pistions and spark melted at E85 pump.

Hello every one.

I'm tuned a 3.0T engine with Garrett 3582 Turbo Boot 34Psi.

E85 fuel and fuel pump keep constant 6.5Bar.

I'm running lambda at 0.83 closeloop, no fuel lean,EGT 780℃, DI injection duration 6.5ms I thought it's not missed injection window.

When 100% GAS MBT ignition only 13 deg will knock,at E85 I push it to 21 deg ,over 21 deg no any power and torque increase so I using 21deg.

On the dyno it's very good running about 30-40 pulls.When it on the street WOT seconds pistion and spark was melted.

Can anyone with experience tell me why it will melted?

@Andre.Simon

When I see this happens, I always think about "what variable changed". If you said every thing was fine on the dyno, what could have changed when on the road. Do you have a log? Was the boost level the same on the road?

In the title, you mention E85 Pump... Did it melt the piston on the same gas tank than on the dyno? I don't know about Japan, but PUMP E85 in Canada is not very consistent, varying from E50 to E85. Were you running a ethanol content sensor?

Also, 0.83 Lambda sounds a bit lean for 34 PSI of boost. But I guess that if you did 30-40 run on the dyno without problems, I guess it shouldn't be the cause. You are mentioning close loop, where you using close loop at full throttle and all the way to the redline?

What do the other pistons and 'plugs look like?

When it's a single cylinder, I would be thinking what could just affect that one, and the most likely is an injector fault - I'd suggest getting the injectors checked for flow. Oh, also, what sort of filtration are you using in the fuel system, as there may be crap on the injector's filter mesh restricting flow?

You say 6.5ms pulse width? for DI, what engine speed you running the engine to, and what are your SOI and EOI limits?

By 3.0T im assuming you mean an Audi V6, so I'm going to use 6700rpm as a reference point.

Cycle time is 17.9ms. Now because it's DI, our injection window isn't really possible for half of the cycle, as this is combustion and exhaust.

This leaves us with 8.95ms for 360 degrees.

Your running 21 degrees timing, so we need to remove 0.52ms from the window (typically you don't want to continue to inject once combustion has started)

Let's say for injection angle reasons, we don't start injecting fuel until 350degrees BTDC to avoid fuel breaching the gas boundary layer and weakening the piston, so we need to remove another 0.25ms, leaving us with a 8.18ms injection window.

A 6.5ms pulse will take 265 crank degrees to inject, so we are injecting until 85 degrees BTDC and igniting at 21 BTDC.

As a decent portion of this is occurring on the compression stroke, the mixture in the combustion chamber will not be vary homogenous.

This leads to uneven temperature across the piston and combustion chamber, plus a slightly adventurous mixture aim for 2.3bar.

There are a few possibilities, with pre ignition occuring - but this usually occurs at sub 3000rpm and advance SOI with higher inlet air temps and E85.

With everything being very 'optimisied' any knock in that combination would be quite devastating

Or uneven combustion has just hot spotted a piston and melted.

Usually over advanced SOI shows in gouging the piston crown, or the piston literally shattering.

@Frank @ Elegant Drift Shop

Yes,close loop at full throttle and all the way to the redline.

@N8B`

My SOI was conservative.

Attached my SOI table.

I have 5 sparks was melded,but only 1 pistion open a hole.

Lambda 0.83 was lean at E85? and cause pre ignition occuring?

Depending on the particular design of the injector and piston, 360 degrees (piston at TDC) is not particularly conservative for SOI - but you may get away with it at high engine speed, although the rest of the table is reasonable.

Your 780c EGT, is that pre or post turbo? You weren't particularly clear. If that's post turbo in the downpipe, I would expect EGT to be 200-300 hotter than that.

0.83LA at that kind of engine load is definitely getting into the hotter combustion temps with ethanol fuel. Did you try try playing around with the fuel mixture aim on the dyno to see how much of an effect it had on power vs egt?

Ok, so you had 5 out 6 plugs fail. What spark plugs are you using in this engine? Even the plugs out of the RS6 (NGK 8 Heat Range) will not be suitable for this engine, I would be wanting to run a non projected, or if i had to, projected 9 heat range NGK race plug.

So even though E85 has good detonation resistance, it is more prone to pre ignition. On a DI engine, at lower engine speeds, where the cycle time is high, more advanced SOI with hotter intake temps means the fuel exchanges a lot of heat, which means the fuel get hot, which when added with the heating up caused by the compression stroke, can cause the ethanol to pre ignite (as alcohol has a lower ignition temp than gasoline) This is why most factory files have aggressive boost limiting down low with high inlet air temps.

Thanks every body.

Its pre turbo.When new engine rebuild,I will try to using 0.78 lambda to running,and 330 SOI and later EOI to test maybe it will be better.