Jochen.Saal Queries:
>Can anybody explain the functionality of the E.G.R valve on the late TR6
Carb?
Quoting from Internal Combustion Engine Fundamentals:
"Exhaust gas recycle (EGR) is the principal technique used for control of
spark ignition (SI) NOx emissions. A fraction of the exhaust gases are
recycled through a control valve from the exhaust to the engine intake
system. The recycled exhaust gas is usually mixed with the fresh fuel-air
mixture just below the throttle valve. EGR acts, at part load, as an
additional diluent in the unburned gas mixture, thereby reducing the peak
burned gas temperatures an NO formation rates. ...Substantial reductions in
NO concentrations are achieved with 10 to 25 percent EGR. However, EGR also
reduces the combustion rate which makes stable combustion more difficult to
achieve."
>From Norman Nocks' Tech Talk:
"This system is fitted to reduce emissions of oxides of nitrogen. The EGR
valve is mounted into the exhaust manifold and controls flow of exhaust
gases into the intake manifold. The control signal is taken from a throttle
edge tapping which gives no recirculation at idle speed or full load, but
gives a varying amount of recirculation between these two extremes depending
on the vacuum signal and metering profile of the valve, A cut-out valve
destroys the vacuum signal to the EGR valve when the choke is operated."
> After I suddenly had idle problems I believe I found the problem in this
>valve.... the piston in the EGR does not fully close.
The valve should be completely closed when no vacuum is applied.
>- When should it be open and when closed?
The factory intended it to be open during partial throttle operations.
>- What happens if I simply close the hole with a plug? (I do not have to
>meet any emission regulation so why not simply remove it?)
If you were to remove it I believe you would join the majority of the late
model TR6 owners with EGR. As Gernot points out you have to reset your
mixture (make it leaner) after removing it. While you are at it disconnect
the vacuum hose to the distributor, the vacuum retard was intended to reduce
hydrocarbon emissions.
In '74 the engineers finally threw in that towel and gutted what little
performance was still left in the engine to meet US environmental
regulations. The anemic compression ratio, EGR and vacuum retard all bear
witness to this fact.
I should note that EGR should in theory decrease fuel consumption. Internal
Combustion Engine Fundamentals states "the "improvement in fuel consumption
with increasing EGR is due to three factors: (1) reduced pumping work as EGR
is increased at constant brake load (fuel and air flows remain almost
constant; hence intake pressure increases); (2) reduced heat loss to the
walls because the burned gas temperature is decreased significantly; and (3)
a reduction in the degree of dissociation in the high temperature burned
gases which allows more of the fuel's chemical energy to be converted to
sensible energy near TC. the first two to these are comparable in magnitude
and each is about twice as important as the third." I actually only believe
(1) because the 7.5 compression ratio is too low to generate much heat or
disassociation.
I have one question for you, what is your commission number? In my spare
time I pretend to be preparing CF12571 for the road!
Thanks
Lee Janssen
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