From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Discussion of theories 'a' and 'b' regarding engine power loss due to fuel vaporisation and nozzle carbon deposits.
| Identifier | ExFiles\Box 179b\3\ img212 | |
| Date | 4th February 1933 | |
| -22- THEORY a.{Mr Adams} In this theory the sudden loss of power would occur when the temperature of the oil in the small chamber at the nozzle tip reached the initial boiling point of the lighter fractions of the fuel. After starting the engine the nozzle would gradually heat up and at first the power would not be affected. As the test proceeded the injector temperature would increase and the initial boiling point of the fuel be approached. The increase in temperature of the fuel would alter the spray and presently the oil would boil, severely disturbing the spray. This would happen quite suddenly and be accompanied by a sudden power drop. This theory received support from the known fact that if a volatile substance such as carbon disulphite is put in the fuel a loss of power results. This theory was checked by the following tests :- (i) Increasing the jacket water outlet temperature to 100°C. (Test 2k). This should increase the tendency for power drop. (ii) Changing fuel to one with lower boiling point (Test 3d). (iii) Using a fuel containing 10% petrol. (Test 3e) The results of these tests did not support the vapourisation theory but (ii) and (iii) were tried when the injector was adequately cooled. If they had been tried without the copper tube in the cylinder head some evidence of vapourisation might have been apparent. It was concluded that with properly cooled injector there was no vapourisation. Theory b. According to this theory the overheated nozzle causes a deposit of carbon to form in or near the nozzle holes. Tests 4g, 4j show that such a deposit was actually formed in the holes and that its removal increased the power. The writer has also experienced similar phenomena on slow speed heavy oil engines having single hole atomisers. If the injection cut-off for any reason was not sufficiently sharp, a dribble resulted which tended to carbonise and build up a trumpet shaped "cone" on the nozzle. This cone might. | ||