For work on compressed natural gas, the engine is aggregated by special equipment . Experience in operating buses with this type of engine has shown that some elements of the power system are subject to the most frequent failures . Based on the information obtained in the process of passing the production practice, a table was constructed in which typical failures and malfunctions of the Cummins engine power system on compressed natural gas are recorded.
Let us analyze the failures presented in the table: a). Failure of the gas reducer with damage to the membrane of the high pressure chamber. The gas reducer for the KamAZ 820.61-260 fuel system is two-chamber, the first chamber lowers the pressure from 200 MPa to 50 MPa, the second – from 50 MPa to 3 MPa . Damage to the membrane is a through-break in the form of a crescent, shown in Figure 8, so that the reducer can not effectively lower the pressure . The cause of this malfunction can be the low power of the built-in heating of the reducer, which is 20 W. Unlike bi-fuel power systems, where the engine starts and warms up on gasoline or diesel fuel, and as a consequence, when the gas supply system is switched on, the reducer is washed with a warm cooling liquid, the KamAZ 820.61-260 engine starts directly on compressed natural gas.
Precisely to prevent freezing of the reducer valves and loss of elasticity of the membranes, a built-in heating is necessary, since with expansion and lowering of pressure the gas is sharply cooled. For comparison, the power of the Landirenzo reducer is 60 W, and there is not a single failure associated with damage to the membrane (based on information received from the individual entrepreneur Kolodyazhny AV). b). Failure of fuel injector with seizure of isolation valve in open position. A frequent reason for the downtime of the rolling stock, in addition to the failure of the spark plugs, is the failure of the fuel injector . The wedging of the nozzle in the open state was presumably due to the skewing of the return spring – the turns of the return spring on one side are worn to metallic shine, while the main spring color is matte, the spring .
Fuel injector malfunction due to leakage. The wear of the saddle-anchor pair has a direct effect on the functioning of the nozzle and the operation of the engine as a whole. As a result of the operation of the fuel injector, numerous damages in the form of concentric circles appeared on the anchor seat, caused, presumably, by a large stroke of the nozzle armature (stroke is 0.63 mm) , so that, when the supply voltage of the injector is disconnected, the anchor on the saddle , sufficient for damage and subsequent leakage loss. The anchor and the nozzle seat.
For comparison, the movement of the anchor of the fuel injectors installed on the Mercedes-Benz 906 LAG engine, which is also designed for operation with compressed natural gas, is 0.17 mm – for the duration of the bus operation, up to 200 thousand kilometers, there was no loss of tightness of the fuel injector (on the basis of information received from the individual entrepreneur Kolodyazhny AV).