in current V6 Turbo era .... which one is more efficient, Log style or Tubular style exhaust ? (in term of installation, performance, heat transfer, exhaust gas flow dynamic....etc)
there are articles explaining about this, but not in term of racing, especially in F1 ......I am very basic in this topic, so i'm hoping some experienced member to give comments ....thanks
It's a pretty big tradeoff, at least from first principles. The advantage of a log is that it is the quickest route between two points, so the exhaust gas arrives hotter. On the other hand the individual pulses from each cylinder are better preserved with individual pipes, and you may even get better pumping efficiency.
They seem to trade in power (and efficiency, as this goes hand in hand in this fuel restricted formula) for a tighter packaging, allowing better aerodynamics.
I really am surprised, as it seems that they do not use the kinetic energy of the exhaust pulsation to power the turbine, but their single entry turbine already pointed to this (unless it's a twin scroll turbine).
To use this energy, the pulses have to be spaced enough and three cylinders are the maximum you can combine if you want to use it efficiently.
It is a complex calculation.
Balancing the benefits of using each exhaust pulse in a primary runner to assist the other primary runners to exhaust more efficiently and place the minimum back pressure on the exhaust valves, against defining the secondary runner length diameter and taper to drive the turbine most effectively.
equal length headers are far FAR more important for NA engine because it will basically make the scavenging work equally for all cylinders, in a turbocharged application though, there is "constant" back pressure on the exhaust side that does the work instead of the individual pulse that would pull/push the scavenging air out and back into the cylinder, the push/pull effect is still there, but its amplitude is so low, that it is simply overshadowed by forced induction and constant back pressure on the exhaust side
p.s. I'm very sceptical about the whole "tuned pulse driven" turbines idea, simply because there is always a drop in the pressure after each pulse, that will "drag" it backwards - thus eliminating the extra push the turbo got from the high pressure pulse, doesn't matter that there is another pulse coming right after from another tube, the drag will cancel out the gain that was achieved by the pulse it was caused by
Pretty good video that explains pulse seperation in turbo exhausts. Also since the Mercedes turbo is expected to be a single entry turbine and not a twin scroll one.
[youtube]http://www.youtube.com/watch?v=T7JTRRlSEYI[/youtube]
The Mercedes manifold looks lige a log type but there is a heatshield covering it so we can't be sure that it isnt 3 seperate smaller pipes running inside.
you cannot cover all the theory (and real world practive) in such a short video, even less so when you generalize the subject
pulses may be all good and nice for a road car turbo spoolup, but for the effective range of the turbocharged-racing-engine, where you actually keep your engine at at all times during the race (and where you want all cylinders to run at equal efficiency), the total mass is the important factor (he even mentions it in the pressure graph there - the area is important, not the max height of the peaks), so the effect simply cancels out for the max power output range of the engine, where the constant pressure between exhaust valve and the turbo acts a damper on any and all pulses
and for an F1 engine, you have the electric motor keeping the turbine up to speed, so spoolup becomes quite irrelevant, same as for other competition turbocharged engines employing all sorts of anti-lag systems
in the first picture to the right, that is not an eqal length header anyway, it looks to me like it was designed with packaging concern in mind rather than an effort to get the pulses "aligned"
jz11 wrote:equal length headers are far FAR more important for NA engine because it will basically make the scavenging work equally for all cylinders, in a turbocharged application though, there is "constant" back pressure on the exhaust side that does the work instead of the individual pulse that would pull/push the scavenging air out and back into the cylinder, the push/pull effect is still there, but its amplitude is so low, that it is simply overshadowed by forced induction and constant back pressure on the exhaust side
p.s. I'm very sceptical about the whole "tuned pulse driven" turbines idea, simply because there is always a drop in the pressure after each pulse, that will "drag" it backwards - thus eliminating the extra push the turbo got from the high pressure pulse, doesn't matter that there is another pulse coming right after from another tube, the drag will cancel out the gain that was achieved by the pulse it was caused by
Ah well I must have been wasting all those years I worked on unequal length headers to improve scavenging and improve power output for OE engines.
All that pipe bending and specialised welding wasted ah well.
No need for those special designed headers fellas just bolt on any old pipe lengths you like.
Tuning today comes from chip tuning and undergrad ideas it seems.
I wrote about the topic - unequal vs equal header doesn't make huge difference for turbocharged engine for reasons I mentioned above, that is all I said, not that any junk will work there, my own experience is not years, but few turbocharged rally engines, and on one mitsubishy 4g63 in particular we replaced header just to see if there was a difference, there was, and it was very faint, might as well be a slight variation in ambient temp (those were different days on the dyno) and the guy that was doing the tuning, that does this for living (and has done it since late 80ties) for competition engines only, grN rally and older generations of grA and wrc cars, rallycross cars etc, NA and turbocharged, confirmed that stock unequal headers work well enough, but if the budged allows, go and get a header made by works teams (which most of time are sort of equal, but not always, usually there is space concern involved in the design), they are more durable and lighter at the same time, but that is like the last upgrade you do to the turbocharged engine
Re tuning turbo response to pulses, I've seen it, and measured it. The turbo spins up and slows down by about 50% in response to the incoming pressure pulses. I only found this out after many months working on a related issue, it killed that project stone dead.
With a V6 engine, there can be interference issues between cylinders sharing the same log-type exhaust manifold due to the long valve durations used on racing cams.
A tuned length 3-into-1 header would be effective on a single turbo V6, since the 3 cylinders in each bank likely have equally spaced firing intervals. Even though the turbo engine intake and exhaust manifold pressures are higher than a N/A engine, the basic acoustic tuning principles still apply.
Using tuned length exhaust headers provides a lightweight, cheap, reliable and compact method of increasing performance.
"Q: How do you make a small fortune in racing?
A: Start with a large one!"
I don't have a great deal of experience with turbo chargers, but the concept of the exhaust 'pulse' intrigues me.
I have a few follow up questions;
- does the low pressure reaction resonate over a time period within the header length or does it decay quickly.
- I am assuming that the junction of headers is calculated to be at an anti node to discourage influencing the other tubes,
- Also are exhaust typically tuned to perform through a narrow or broad rev range?
Ignoring the low pressure reaction, I also assume that the turbo's rotational inertia is carefully designed as to provide 'mass dampening' to excitation throughout the desired rev range.
If this is the case, then it opens the door for some clever use of the MGU-H in helping to dampen the fluctuations in the turbine speed by regeneration. I would imagine that this is quite achievable, giving them the benefits of stabilising the turbine speed to fluctuations in rotational velocity by dampening out the peaks and regenerating power from the smoothed response.
"I continuously go further and further learning about my own limitations, my body limitations, psychological limitations. It's a way of life for me." - Ayrton Senna
Robbobnob wrote: I would imagine that this is quite achievable, giving them the benefits of stabilising the turbine speed to fluctuations in rotational velocity by dampening out the peaks and regenerating power from the smoothed response.
What type of fluctuations are you talking about? For example: the slight drop in pressure between individual cylinders firing?
