However, at 1,220 revolutions it was found that the quantity of
oil employed appeared to have a distinct effect upon the mechanical
(friction) losses, and it was therefore necessary to maintain an
ample supply of lubricant.
* " Test of a Daimler Sleeve Valve Engine," Proc. I.A.E., 1912.
170 HIGB SPEED INTERNAL COMBUSTION ENGINES



300



200 —



The Pumping Losses.
By the pumping losses in any engine is meant the work which
is done (at the expense of the indicated horse power) in the induc-
tion or drawing in of the fresh charge and in the expelling of the
exhaust products.
Generally, the pressure within the cylinder during the suction
stroke is below atmospheric, whilst the pressure of the exhaust
products is above atmospheric.
The amount of " negative work " which has to be performed
in the exhaust and induction operations is a measure of the
pumping losses, and is represented by the area of the suction-
exhaust loop on the indicator diagram, as shown shaded in Fig. 74.
As was previously
pointed out, these
losses in a car engine
amount to between 10
to 20 per cent, of the
total losses between the
indicated and brake
horse power.
It has also been
shown that the tem-
peratvire existing within
the cylinder has an
influence upon the
quantity of air and
petrol drawn in per
suction stroke, and here it might be added that the resistance to
motion of heated air, or exhaust gases, is less than in the case of
cool air.
Considering the influence of speed upon the pumping losses,
these losses will increase with increased speed, owing to the greater
wire-drawing or throttling of the gases flowing at higher speeds.
