Mercedes Power Unit Hardware & Software

[ringo]

If this engine is basically a diesel engine, it's efficiency is not really all that groundbreaking. lol

[bergie88]

I don't know anything about that source but it seems to me that the author has taken the idea that Mercedes (the actual mercedes) have been doing HCCI research for a decade and taken the idea that HCCI is efficient and suspected vibration issues and decided that Mercedes HPE are using HCCI in their F1 engines. What is the actual evidence/source that Mercedes HPE are using HCCI? Furthermore, does it even make sense to have HCCI combustion in an F1 engine?

Combustion efficiency?

[Brian Coat]

Combustion efficiency is usually a measure of how effectively the heat content of a fuel is transferred into usable heat and this will be about 100% already.

I think that the potential gains from full load HCCI/CAI might stem from the potential (?) ability to run a higher cycle pressure ratio but avoid/mitigate the conventional fuel/knock limitations associated with high pre-combustion pressures and temperatures?

A more conventional development path would be to retain conventional combustion and develop the fuel or other engine parameters to mitigate knock and allow a higher cycle pressure ratio.

In either case, I imagine the peak cylinder pressures and peak rate of pressure rise start to get pretty exotic.

[gruntguru]

I think that the potential gains from full load HCCI/CAI might stem from the potential (?) ability to run a higher cycle pressure ratio but avoid/mitigate the conventional fuel/knock limitations associated with high pre-combustion pressures and temperatures?

Spot on. HCCI benefits two of the key metrics for efficiency:

1. Rapid combustion. The (unattainable) holy grail is for all combustion to occur at TDC as in the idealised Otto cycle.

2. High compression and expansion ratio. HCCI reduces detonation of the end gas by initiating combustion at multiple sites.

[Tommy Cookers]

there's nothing wrong with some detonation of the end gas (except in a showroom demo drive etc)
eg WW2 and the Le Mans 24 hr etc were won with detonation in the end gas
it's showing that the engine is a compromise and non-ideal to 21st century eyes

but to the extent that the engine can survive the diluted and earlier detonation that is called CI or HCCI .....
eg HCCI allows the use of a greater CR and expansion (than would SI) and this improves efficiency

[dmjunqueira]

Just sharing an old publication about Mercedes's Diesotto prototype engine...Maybe there is something to do with the technology supposedly applied on F1 engine.
http://www.telegraph.co.uk/motoring/gre ... l-mix.html

[dren]

That's based on varying the crank geometry to alter CR. I think that's against the regs?

[PlatinumZealot]

Mercedes still have a whole lotta knock according to the engineers... In fact all the engines do. Not sure if this means the engines are almost dieseling or not...

[hurril]

Mercedes still have a whole lotta knock according to the engineers... In fact all the engines do. Not sure if this means the engines are almost dieseling or not...

But what is this talk about a single knock being able to basically blow the engine to smithereens?

[gruntguru]

Talk.

[gruntguru]

there's nothing wrong with some detonation of the end gas (except in a showroom demo drive etc)
eg WW2 and the Le Mans 24 hr etc were won with detonation in the end gas
it's showing that the engine is a compromise and non-ideal to 21st century eyes

but to the extent that the engine can survive the diluted and earlier detonation that is called CI or HCCI .....
eg HCCI allows the use of a greater CR and expansion (than would SI) and this improves efficiency

Detonation is an inefficient process. The shock wave causes increased heat loss to the walls and of course thermal and mechanical damage in extreme cases. Some detonation can be tolerated in a trade-off with efficiency/power gains from increased CR, boost, leanness etc.

HCCI in itself is not detonation. It is temperature initiated combustion. It is often accompanied by detonation which is probably better tolerated because of the multiple sources and shockwaves, their small magnitude and cancellation effects.

[Brian Coat]

So we all appear to agree that knock is a bad thing which can allow good things to happen and so can be tolerated at moderate levels - a bit like drinking alcohol

At 'only' 10-15K rpm can we expect that some piston weight will be traded for piston strength(/cooling?) to improve knock tolerance/resistance?

If so, how far do we think engine teams will have taken this?

[Facts Only]

Mercedes still have a whole lotta knock according to the engineers... In fact all the engines do. Not sure if this means the engines are almost dieseling or not...

Which engineers are saying that?

[PlatinumZealot]

Pat symmonds or one of the mercedes guys. I don't remember right now.. but the person said that detonation was a key thing they have to tune for. It must be in the end of year petronas video or something.. sigh... I will have to find that now..

start from here: http://www.skysports.com/f1/news/32420/ ... cy-in-2015

I will try to find the source in the mean time.

[Powerslide]

I don't know anything about that source but it seems to me that the author has taken the idea that Mercedes (the actual mercedes) have been doing HCCI research for a decade and taken the idea that HCCI is efficient and suspected vibration issues and decided that Mercedes HPE are using HCCI in their F1 engines. What is the actual evidence/source that Mercedes HPE are using HCCI? Furthermore, does it even make sense to have HCCI combustion in an F1 engine?

i doubt they could get hcci to operate in such volatile circumstances with the combustion and boost temperature of a formula one engine. hcci is one technology that might make it to normal engines first before race because it has a sensitive operating load area. they could not get it to work when load is too low and becomes very unpredictable when load is high. hcci is natural combustion, treating the air fuel mix before it detonates by its self, unlike diesel. By doing this, burning would not be a problem as every mixed element would get ignited by temperature rather than spark or an injector, avoiding requirement of a little spot to start the process. localized? a rather stable environment or predictable environment is required, probably not in a formula one engine although I think it has a rather desirable manifold pressure to bmep return