A diagrammatic representation of a Still engine of the two-cycle heavy-oil type is shown in Figure 54. This is shown with an auxiliary boiler heated by an oil burner. The piston of this engine has a sleeve which fits into an annular steam cylinder. The latter is an extension of the combustion cylinder. Surrounding the steam and combustion cylinders are the steam and water jackets. The drawing shows the piston at the end of its downward stroke, having just been driven down by the gases of combustion. In this position a scavenging-air port at the left is uncovered and the burnt gases are swept out by a blast of air, passing out of the exhaust. This consists of a bank of tubes or flues which pass through a water heater. The gases leave the cylinder with a temperature of 900 degrees Fahrenheit and they issue from the exhaust with a final temperature of only 150 degrees Fahrenheit. Steam now enters the annular steam cylinder from the steam jacket, through the port shown at the lower right-hand side, forcing the piston up and compressing the charge of air in the cylinder. Then oil is sprayed in through a nozzle, not shown in the drawing, and is ignited by the heat of the compressed air as in a Diesel engine and the piston is driven down again by the gases of the combustion. The water surrounding the combustion cylinder comes from the lower part of the boiler and flows by the exhaust flues. It is maintained at a temperature of 350 degrees in the water jacket, and here is turned into steam by the heat of the combustion. Thence it passes into the steam dome of the boiler. On the downward stroke of the piston a slide valve, shown at the lower right-hand side, moves down and connects the steam port with an exhaust port through which the steam flows out into a condenser. Water from the hot well of the condenser enters the system at the combustion exhaust. The arrows show the course of the steam and water and the temperature at various points is given. As may be noted there are two systems of steam and water circulation: one from the bottom of the boiler through combustion exhaust heater to the water jacket and back to the top of the boiler; and the other from the steam dome of the boiler to the steam jacket, to the steam cylinder, to the steam exhaust, to the condenser and back again from the condenser into the combustion exhaust heater, whence it enters the boiler by way of the water jacket. LATENT HEAT