Let us imagine ourselves inside the cylinder of a Diesel engine, seated confortably on the top of the piston, at or about the end of the compression stroke. We are in complete darkness, the atmosphere is a trifle oppressive, for the shade temperature is well over 500C, and the atmosphere is very dense. Also it is very draughty, such that in reality we would be blown off our perch and hurled about like autumn leaves in a gale.
Suddenly, above our heads a valve is opened and a rainstorm of fuel begins to descend. In fact, the velocity of droplets approaches much more nearly that of rifle bullets than of raindrops! For a while nothing startling happens, the rain continues to fall, the darkness remains intense. Then suddenly, away to our right a brilliant gleam of light appears, moving swiftly and purposefully; in an instant, this is followed by a myriad others all around us, some large and some small, until on all sides of us the space is filled with with a merry blaze of moving lights; from time to time the smaller lights wink and go out while the larger ones develop fiery tails like comets; occasionally these strike the walls of the cylinder but being surrounded with an envelope of burning vapour they merely bounce off like drops of water spilt on a red hot plate.
Right overhead all is darkness still, the rainstorm continues and the heat is becoming intense; now we shall see that a change is taking place. Many of the smaller lights around us have gone out, but new ones are beginning to appear, more overhead, and to form themselves into definite streams shooting rapidly downwards or outwards from the direction of the injector nozzles. Looking around again, we see that the lights around are growing yellower; they no longer move in definite directions but appear to be drifting listlessly hither and thither; here and there they are crowding together on dense nebulae and these are burning now with a sickly smoky flame, half suffocated for want of oxygen.
Now we are attracted by a dazzle overhead, and looking up, we see that what at first was a cold rain falling through utter darkness has given place to a cascade of fire as from a rocket. For a little while this continues, then ceases abruptly as the fuel valve closes. Above and all around us are still some lingering fireballs, now trailing long trails of sparks and smoke and wandering aimlessly in search of the last dregs of oxygen which will consume them finally and set their souls at rest.
So ends the scene, or rather my conception of the scene, and I will ask you to realise that what has taken me nearly five minutes to describe may all be enacted in one five-hundredth of a second, or even less.
Sir Harry Ricardo lecturing to the Royal Society, 23 November 1931
(76 years ago tonight)
