Temperature Dependence of Carbon Deposit in a Diesel Combustion Chamber

In order to prevent carbon deposits in the combustion chamber of a diesel engine, it is recommended to avoid direct impingement of fuel on the wall of combustion chamber, though it may sometimes be impossible. In this report, the present authors examined how the carbon deposits were dependent on the wall surface temperature of the combustion chamber in the case where fuel spray impinged directly on the wall. For this purpose, a probe on which the spray impinged was set in the prechamber of the testing engine and thereby the relation between deposits and wall temperature was determined. The test results are summarized as follows : The deposits increase with time at a constant rate at first and, when it exceeds a certain limit, the deposit lump is removed off the probe. With the fuel employed in the test, the deposit reached a maximum at 200°C. Above 550°C, the amount of the deposit is only about one thirtieth the quantity at 200°C. This is because inadhesive deposits are produced at a high wall temperature owing to thorough cracking.