combustion space

Boxer engines must not be confused with opposed-piston engines, which are essentially the inverse, with two pistons compressing a single combustion space.

The roaster consists of a refractory-lined cylindrical steel shell, with a large combustion space at the top and 2 to 4 hearths in the lower portion, similar to those of a multiple hearth furnace.

Few electric start models - Lister-Petter, Yanmar, or Chinese types - need any additional starting devices as 1-2 seconds cranking injects enough unburnt Diesel into the combustion space above the piston to boost the compression automatically and quickly.

Because of their heat-retaining design, the size of valves and the compression ratio are limited (the valve/combustion chamber is away from the piston top typically creating a larger combustion space--a lower compression ratio), which in turn reduces available power and economy.

The boiler was interchangeable with the T9 class, and likewise was equipped with water tubes fitted across the firebox combustion space, with the aim of increasing heating surface whilst facilitating water circulation; this device however also increased maintenance costs and was soon removed by Drummond's successor, Robert Urie.