Flow Characteristics of a Gas-Blast Fuel Injector for Direct-Injection Compression-Ignition Engines 2009-01-1857
Natural gas has a high auto-ignition temperature, therefore natural gas engines use sparks, hot surfaces or separate diesel pilot injects to promote ignition. For example, the high-pressure direction-injection (HPDI) system, available commercially for heavy-duty truck engines, uses a small diesel injection just prior to the main gas injection. A new type of HPDI injector has been developed that injections diesel and gas simultaneously through the same holes. In this paper the operation and flow characteristics of this “co-injector” will be discussed.
An injection visualization chamber (IVC) was developed for optical characterization of injections into a chamber at pressures up to 80 bar. A fuel supply system was constructed for precise control of injector fueling and injection timing. Diesel and natural gas are replaced by VISCOR ® and nitrogen to study non-reacting flows. A novel feature of the IVC is a retracting shroud that allows the injector to reach steady-state prior to imaging, without fouling the IVC windows.
Results indicate the mechanical delay of the developed injector is independent of chamber backpressure. However, for constant commanded injection duration, gas injection quantities are increased by higher chamber backpressure and decreased if the liquid mass injected is increased. These results are compared to theory using an AMESim model developed for an existing production injector. Changes in the gas/liquid ratio (as measured by the fluid supply system) are reflected in different jet image characteristics.