Race Tech Magazine had an interesting article on sequential
turbo charged diesel engines for the Dakar race.
www.racetechmag.com

The article made it sound like VW invented the sequential
turbo when Mazda had them on the Cosmo 3 rotor turbo and the 1993 to 2004 RX7
two rotor. PL

"Before we examine the reasons why, we must look a little closer at those
few FIA Cross Country engine regulations that exist.
The gist of Appendix j, Articles 282 and 285 for Tl cars, is that
other than having to breathe through a single 39 mm diameter restrictor,
the capacity of the engine is totally 'free' and not limited in any way."

If the silly race organizer insist on an intake air restrictor it is better to have
a turbo charger sucking air through the restrictor than having a normally
aspirated engine. That is because the air flow through a restrictor is proportional
to the pressure difference across the restrictor up to a point. Probably
that point is supersonic flow. PL

"If you have a turbocharger then you need to take account of the 1.5 factor to
select the minimum vehicle weight but, apart from this, two-stage turbocharging
is not only tolerated but actively promoted.  "An important part of the regulations
is the statement that no [exhaust] smoke is to be visible at any time," says Winchelhaus.
"But, seemingly not helping, rt diesel particulate filters (DPFs) are specifically outlawed.""

"Especially so as exhaust smoke effectively limits your air:fuel ratio and
hence brake mean effective pressure." Clearly combustion and its
cleanliness are critical issues in a racing diesel."

This limits the acceleration of any diesel engine as the way you accelerate a diesel is
feed it excess fuel which results in carcinogenic black smoke. You can see this
in any video of a diesel tractor pull.

http://www.youtube.com/watch?v=F1VpJOXbzBI
http://www.youtube.com/watch?v=w3Oym5CbeJk

Fortunately gasoline engines and turbines have almost replaced diesel
engines in tractor pulls. PL


"Because they need more power at Le Mans, the LMPl regulations relate the engine
capacity (between 4.0 and 5.5 litres) to the maximum boost pressure.  However, a diesel
particulate filter is mandatory and this makes a huge difference. Your combustion can
be a bit smoky and the diesel particulate filter will remove these smoky excursions,
enabling you to fuel nearer the smoke limit. The downside is that the high back pressure
created by the filter placed after the turbocharger turbine will result in lower
turbine efficiencies and so any high boost concept makes little sense."

"If we compress the gas in two stages and introduce a cooler between the two stages,
you will end up with a lower charge temperature than just the single turbo case."
Indeed, as any thermodynamics expert will tell you, not only is the work done to
compress a gas in two stages more efficient but the introduction of an intercooler
mid-stage reduces the charge temperature even further. As Winchelhaus states,
"Two-stage turbocharging without intercooling makes no sense at all.""


Lemans 24 hour race is coming up soon so we will all see first hand yet again why the French
are rationalizing the European excess and tax subsidized use of diesel powered cars by
overly favoring diesel powered Lemans race cars mis-using  the race regulations.
Consequently the credibility of the Lemans race will yet again be damaged.

How the mighty have fallen.

If they want to achieve a social good they should allow turbo compound engines
to be competitive and go back to a race fuel quantity limit.