CRANKING POWER and TORQUE REQUIREMENTS at SUBZERO TEMPERATURES 430146
THE inescapable conclusion of Mr. Knudsen is that an immersion heater is required for the starting of diesel engines at subzero temperatures. “With this method,” he says, “the danger of scoring and scuffing pistons and cylinders during the cranking period due to improper oil films is removed. The engine can be started with the lubricating oil most suitable for it at operating temperature. Cranking power requirements are no greater than in the summertime, so the batteries need not be excessively large for winter starting - even the batteries might be kept up to temperature by an immersion heater, and hence a further reduction in weight and capacity would be possible.”
Mr. Knudsen resolves the problem of subzero starting into several parts:
The fuel oil must be able to flow freely at starting temperatures.
Lubricating oil must be available that permits cranking at about 100 rpm at the desired starting temperature with reasonable starting-power requirements.
Starting-power requirements must be such that they may be satisfied by batteries of reasonable size and weight.
Engine characteristics must be such that ignition temperatures for the fuel available will be reached within the combustion chamber when cranking at minimum starting rpm for the engine in question.
Tests were made to determine the starting power requirements at various temperatures with different grades of lubricating oils. These tests indicated that cranking power can be reduced by diluting the lubricating oil with kerosene or similar agents, but such a solution would be unsatisfactory.