Hi Lee,
thanks a lot for your good explanation of the EGR valve functionality.
My comm.-no. is CF24535
regards,
Jochen
Janssen, Lee K wrote:
> 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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