The CNG-di system is operating at low feed pressure of 20 bar to avoid separate CNG compressor and utilise fuel tank capacity for acceptable driving range. This comparable low feed pressure is sufficient to directly feed the injection spray during compression stroke into the combustion chamber, but the injector requires quite big metering orifices to enable required gas quantities. As long as no injectors from series application have been available, a special AVL prototype injector has been used during development of the combustion system.
Features of AVL prototype CNG injector:
The injector was applied with different nozzle geometries to vary gas-jet angles during course of the project. The nozzle geometry even was suitable for the increased compression backpressure with charged engine operation.
This injector is a first functional prototype and gave important engine results for the outward opening injector concept. A Piezo actuated outward opening injector by Siemens with comparable valve geometry will be used for future investigations at DC when transferring the combustion system to a 4 cylinder engine.