A piston and cylinder arrangment for an internal combustion engine designed to run on diesel and similar fuels, comprises a cylinder defining a main combustion chamber, a piston reciprocatable within said cylinder and having a thermally insulating plate on its upper surface, a cylinder head including a precombustion chamber, a fuel injector for injecting fuel into said precombustion chamber, and a thermally insulated block of material with high heat retention ability surrounding the precombustion chamber to maintain a high temperature a high temperature of at least about 500.degree. C. in the precombustion chamber and thereby facilitate fuel ignition at moderate compression ratios. A mass of material with high heat retention ability is mounted on the insulated surface of the piston so as to remain at a high temperature during running of the engine and facilitate the combustion process during the downward stroke of the piston.