RE: GAS-L: Wasted throttle power

[Weststeijn A <A.Weststeijn@epz.nl>]

On the subject of variable compression of combustion engines:

Kevin wrote:

> >The conceptually simple way to make an Otto Cycle engine efficient over a
> >range of loads is to vary the engine displacement, rather than keeping
> >displacement constant, and varying the compression ratio. One way to do
> this
> >is disable/enable cylinders in a multi cylinder engine, while keeping
> fuel/
> >flow to the operating cylinders constant.
> 
Andrew Heggie [SMTP:andrew.heggie@dtn.ntl.com]
replied 20 februari 2001 2:35
on enabling/disabling cylinders:

> This is done on the larger Daimler Benz engines, not easy to implement
> in the absence of fuel injection. Also some problems with keeping
> internal surfaces hot and pumping losses, you have to cycle some air
> otherwise there are problems with sealing I think.
> 
Peter Singfield tipped off the Cadillac engine with enabled/disabled
cylinders.

Now, for a true example of variable compression check out the new SAAB
engine recently introduced on the market.

I don't drive one so I can't say whether the claim of reduced fuel
consumption by 30% is real.
But parameters of 225 bhp and 305 Nm (225 lbfeet) torque, for a mass
produced 1.6 liter (98 cu-inches!) engine sold in the regular car market,
are impressive by any standard!

http://www.saab.com/home/GLOBAL/en/index.xml
(choose subweb "Saab Variable Compression"

QUOTE

SVC - a unique new engine concept

> Saab is now launching an entirely new engine concept named SVC, which
> stands for Saab Variable Compression. Owing to the SVC engine's unique
> design, it offers performance on a par with units twice its size but with
> the fuel consumption of a small engine. The SVC engine is a five-cylinder
> 1.6 litre unit producing 225 bhp, and it delivers no less than 305 Nm of
> torque.
> 
> What is unique about the SVC engine is that it features variable
> compression. In other words, the ratio between the piston's displacement
> volume and the volume of the combustion chamber is not constant, as it is
> in a conventional engine. Instead, the SVC registers current needs and
> decides how much the mixture of fuel and air is to be compressed in the
> cylinder prior to ignition. The upper part, the mono-head, can be inclined
> up to four degrees to achieve optimum compression, which means that the
> engine always works at its most efficient level.
> 
It is this variable compression in combination with considerable overboost
and a scaled-down cylinder displacement that makes the SVC design so strong
and at the same time so fuel-efficient. Generous overboost means it is
possible to supply more fuel to the engine as and when needed. This in turn
promotes both greater torque and higher power output. A smaller cylinder
displacement also means the engine is lighter and operates with lower
friction, so it uses fuel more efficiently compared to a conventional
engine. Fuel consumption can be reduced by up to 30 percent - while
retaining existing performance levels.

UNQUOTE


best regards,
Andries Weststeijn