Facility for Heating the Fuel

Various solutions were contemplated for varying fuel temperature. In an initial approach, consideration was given to heating the entire volume in the fuel reservoir. On the one hand, this would mean that the fuel, heated to over 400°C, would have had to pass through the entire injector, severely impairing its durability on account of the material combination present in the injector. Furthermore, it would have been virtually impossible or extremely complicated to maintain the temperature over the running length from volume to nozzle tip as the heat lost from the large, overall surface would have been too high.

Consequently, an approach was selected that uses a kind of continuous-flow heater to heat the fuel directly upstream of the nozzle tip. To this end, a small heating coil was applied directly to the nozzle shaft, Figure 14. This mode of procedure made sure that no destructively high temperatures ever occur in the injector — which was additionally assisted by a cooling unit between heater and the rest of the injector. With this approach, it can furthermore be assumed that the injected fuel also has the same temperature as that of the fuel in the nozzle shaft.

Injector cooling unit heating coil

Facility for Heating the Fuel

Pressure sensor rail

Figure 14: Heating coil on the injector

Nozzle-shaft temperature was monitored by a type K thermocouple applied directly to the nozzle shaft.

Figure 15: Injected mass over period of GDI injector actuation before and after high-pressure testing

подпись: 
figure 15: injected mass over period of gdi injector actuation before and after high-pressure testing
Heat transfer was improved by additionally applying a heat-conducting paste between shaft and copper ring as well as between copper ring and heating element. Maximum heat output is 200 W, with the heating coil’s maximum attainable temperature being 700°C. Altogether, the facility was designed and fitted in a way that allows the injector to be calibrated on the pressure chamber without any major problems.

The state of the injector was recorded before and after the measurement campaign by measuring linearity. A comparison of these measurements is shown in Figure

15.

The results of the measurements, conducted at two different injection pressures with IAV’s Injection Analyzer, confirm that the injector remains in perfect working order after completion of the measurement campaign too. It can be deduced from this that a solution similar to this variant for pressure-chamber testing could also be implemented for engine tests without damaging the injector.

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