Renault Power Unit Hardware & Software

[Tommy Cookers]

wouldn't you want to run the spark as a backup with HCCI transition/de-transition anyway? - so fulltime sparking is likely ?

the SIDI - in CI mode must have heated the charge to enable CI by using internal EGR via VVT ?
in F1 charge heating enabling HCCI must come from 'internal EGR' via raised exhaust pressure producing a small controlled under-scavenge ?

as well as the rumoured so-called HCCI, might we not contemplate PCCI aka PPCI ?


btw - 5.6 g 'braking' at Monza is about 4 g from the brakes, the rest aero and mech drag and uncorrected attitude/overshoot effects etc ?
and of course with 5.6 g deceleration the speed plummets, the DF and grip plummet, and the brake power plummets
(yes, I have suggested raising the MGU-K power)

[FW17]

EGR and VVT are not permitted

[Tommy Cookers]

that's why F1 can get the same effect in another way

the exhaust pressure relative to the induction pressure aka boost is under continuous control via the (electrical) loading to the mgu-h
that exhaust pressure determines the amount of combustion product (if any) that remains in the cylinder after the exhaust stroke
a few % of that product remaining will have a big effect on the temperature the next charge reaches when compressed by the piston
if that temperature reached is sufficient for (HC or whatever) CI there will be CI

so CI can be applied or removed as required
assuming it must be removed at high fuel rates or we will wreck the engine with excessive peak combustion pressure
EDIT (later decided that we won't wreck the engine if we have a very high AFR 'diluting' the peak conditions)

an engine that is made unwreckable in that way it is generally called a diesel
the minimum octane number allowed for F1 fuel is 75 - presumably to keep the diesel out

[R_GoWin]

In another forum, a member claims that HCCI is illegal as all combustion must be initiated by a spark plug. I feel that this would be impossible to police, as pre ignition happens all the time. As long as the plug is still fired at sometime in the ignition process.
Thoughts?

There is nothing in the technical regulations that determines how combustion should be initiated, or outlawing HCCI. Although I can see where the confusion could come from - the closest it comes to addressing this is via regulations to ignition systems:

5.11 Ignition System
5.11.1 Ignition is only permitted by means of a single ignition coil and single spark plug per cylinder. No more than five sparks per cylinder per engine cycle are permitted. The use of plasma, laser or other high frequency ignition techniques is forbidden. Only approved ignition coils may be used and the list of parts approved by the FIA, and the approval procedure, may be found in the Appendix to the Technical Regulations.

I would read that as a regulation for number of coils and components used for ignition system, rather than a regulation to control the physics of ignition. (spark ignition rather than auto-ignition).

It also says upto 5 sparks are permitted. No spark or 0 spark is not dealt with in the rule book.

[R_GoWin]

This link talks about a boosted HCCI system without knock. Pretty interesting.
http://energy.gov/sites/prod/files/2014 ... 09_dec.pdf

Having gone through it, some takeaways for me are:

- Higher CR is a requirement for auto-ignition and hence becomes an advantage when the system could be controlled to work, as this gives higher thermal efficiency.
- They've achieved an indicated thermal efficiency of ~45 to 47% and an IMEP of 16.3 bar with 87 -ON gasoline.
- Achieving high power it is limited by knock, and is the limiting factor for HCCI.
- But its pretty interesting how they define knock (knock-limit criterion). The presentation makes a distinction between ringing and knock, which seems to suggest that these engines always operate with oscillations in rate of in-cylinder pressure rise (and some ping-ing sound), Ringing intensity of upto 5MW/m2 is not considered knock. And as boost increases, this increases the rate of pressure rise(faster combustion) allowable for ringing.
- The 'HCCI' name is increasingly looking like a misnomer. The presentation stays clear of advance ignition to prevent knock. (although F1 team may want to push those boundaries). Retarded ignition will not allow sufficient time for fuel vapour to reach suitable homogeneity and will be stratified. So I think what we may effectively have in reality is a range of auto-ignition modes - HCCI to SCCI to PCCI (as Tommy Cookers says).

[zac510]

In another forum, a member claims that HCCI is illegal as all combustion must be initiated by a spark plug. I feel that this would be impossible to police, as pre ignition happens all the time. As long as the plug is still fired at sometime in the ignition process.
Thoughts?

There is nothing in the technical regulations that determines how combustion should be initiated, or outlawing HCCI. Although I can see where the confusion could come from - the closest it comes to addressing this is via regulations to ignition systems:

5.11 Ignition System
5.11.1 Ignition is only permitted by means of a single ignition coil and single spark plug per cylinder. No more than five sparks per cylinder per engine cycle are permitted. The use of plasma, laser or other high frequency ignition techniques is forbidden. Only approved ignition coils may be used and the list of parts approved by the FIA, and the approval procedure, may be found in the Appendix to the Technical Regulations.

I would read that as a regulation for number of coils and components used for ignition system, rather than a regulation to control the physics of ignition. (spark ignition rather than auto-ignition).

It also says upto 5 sparks are permitted. No spark or 0 spark is not dealt with in the rule book.

I thought the "Ignition is only permitted by means of..." part seemed to me fairly clear that the spark plug is the only thing that's allowed to ignite the fuel/air mix.

[FW17]

- Higher CR is a requirement for auto-ignition and hence becomes an advantage when the system could be controlled to work, as this gives higher thermal efficiency.

How does that explain 2 stoke engines auto ignition?

Chamber temp can be controlled by variable coolant, incoming air and fuel temperature

[R_GoWin]

- Higher CR is a requirement for auto-ignition and hence becomes an advantage when the system could be controlled to work, as this gives higher thermal efficiency.

How does that explain 2 stoke engines auto ignition?

Chamber temp can be controlled by variable coolant, incoming air and fuel temperature

Well, you are right. You could change those things to induce auto-ignition. And apart from that I do think you also need to trap some hot burnt gas residuals to help with in-cylinder temperature rise for auto-ignition. But the way I see it is: if you are not going to bump up the CR and reap the benefits of greater thermal efficiency that comes with compression ignition - painstakingly developed to work like a diesel in a gasoline engine - then why bother with developing that technology in the first place?

[gruntguru]

- Higher CR is a requirement for auto-ignition and hence becomes an advantage when the system could be controlled to work, as this gives higher thermal efficiency.

Chamber temp can be controlled by variable coolant, incoming air and fuel temperature

Well, you are right. You could change those things to induce auto-ignition. And apart from that I do think you also need to trap some hot burnt gas residuals to help with in-cylinder temperature rise for auto-ignition. But the way I see it is: if you are not going to bump up the CR and reap the benefits of greater thermal efficiency that comes with compression ignition - painstakingly developed to work like a diesel in a gasoline engine - then why bother with developing that technology in the first place?

Compression ignition with burn rate limited by controlled fuel admission (diesel cycle) does not produce greater thermal efficiency, in fact the opposite is true - Otto cycle is more efficient than Diesel for a given CR. The higher CR possible with controlled-rate combustion is one part of the diesel's efficiency advantage. (I think you are aware of this but have not made it clear in your post.) The other two parts are lean AFR and absence of part-load throttling.

The CR of the current F1 engines is not known but I am certain that it is at least as high as would be possible with a Diesel cycle at the same specific output. This can be inferred from the very high peak cylinder pressure claimed by Mercedes.

Why bother with CI in the first place? Not CI "like a diesel" but HCCI (or something similar) - the advantage being, rapid combustion near TDC, (approaching the ideal Otto cycle) made possible by multiple combustion sites, and relatively damage-free detonation due to the very short paths for each shock wave to develop intensity. "Normal" SI detonation is damaging because shock-initiated-combustion is able to traverse the entire end-gas region and develop to a high intensity before striking the surfaces of the combustion chamber.

[gruntguru]

wouldn't you want to run the spark as a backup with HCCI transition/de-transition anyway? - so fulltime sparking is likely ?the SIDI - in CI mode must have heated the charge to enable CI by using internal EGR via VVT ?
in F1 charge heating enabling HCCI must come from 'internal EGR' via raised exhaust pressure producing a small controlled under-scavenge ? as well as the rumoured so-called HCCI, might we not contemplate PCCI aka PPCI ?

Thermodynamically speaking, increased CAT would be preferable to EGR. EGR robs hot gas-flow from the turbine whereas increased CAT reduces heat lost at the intercooler and makes that heat available to the turbine.

EGR controlled by the MGUH would have a slow response. CAT can be controlled very rapidly to cope with transients by throttling hot air bypassing the intercooler. Auto ignition can also be controlled by throttling the intake itself provided the AFR doesn't depart too far from ideal.

BTW - has anyone seen any pipework that could be an intercooler bypass - running from compressor to intake manifold?

[Brian Coat]

A few thoughts/questions based on the recent HCCI discussion.

1. Don't All HCCI engines use spark plugs? I see no rules issue.

2. Given that we don't care about emissions etc. , what does the EGR dilution route offer that air (enleanment) does not? Especially as enleanment is desirable for raising OPR.

3. Why is raising the air charge temp discussed as necessary for HCCI at this speed and load ? Have we seen anyone needing to do this at full load?

[NL_Fer]

Would the standard ECU be able to steer such complex combustion?

[gruntguru]

Would the standard ECU be able to steer such complex combustion?

As long as the std ECU is capable of controlling one additional actuator - a variable intercooler bypass.

[Tommy Cookers]

so-called HCCI running at full power ? ......

the fuelling will be dispersed using the available time window, fuel will be dispersed spatially and in exposure time
so CI initiation will be dispersed in time, and so peak pressure will be contained to a tolerable level
ie combustion will be as fast as possible but never too fast

surely residuals are anyway prevalent (with recovery) in a way that was uknown with the more favourable pressure differences in N/A engines ?
control by managing residuals and/or by managing CAT ? - the response time of either will be a few tens of milliseconds only
(as per gg's earlier figures) raising exhaust pressure (slightly above induction pressure) has a great benefit to recovery
the HCCI paper linked yesterday by R GoWin states that such raised exhaust pressure was acceptable to their engine
if managing CAT would we need a cooler at all ?


and ...... does full power mean eg full power 10500 rpm or full power 12300 rpm ?

above 10500 the energy state in-cylinder falls as the fuel rate doesn't rise with rpm
boost pressure or AFR or both will fall with rpm
raising the residuals would then boost that energy state and also benefit recovery
and help to maintain combustion speed
(this I suggested years ago, assuming SI)
the above 10500 zone of operation is important

[PlatinumZealot]

I think EGR option is very limited because there is no variable valve timing or valve lift allowed.

Anyway this last race I saw a Renault Engine powered car overtake a Williams. Renault is definitely over 900hp now. Cannot be denied anymore. I am looking forward to the upgrade for sure.