To achieve realistic gas temperature and pressure in spray-study bombs, both precombustion and rapid-compression machines are used frequently.
This paper describes an alternative concept for achieving the desired gas conditions. The gas intended for the spray study is pre-heated to 660°C in an external heated vessel made of a heat-resistant alloy. Prior to injection, the heated vessel is connected to the spray bomb via a new fast-opening valve located inside the bomb, and the hot gas fills the bomb rapidly.
For convenient actuation of unit injectors in laboratory set-ups, a new hydraulic-based actuation system was developed. An eccentric drives a hydraulic piston. A second hydraulic piston actuates the unit injector. A range of injection pressure histories, i.e. rate shaping, can be obtained. The stiffness of the hydraulic system is compared with the normal cam - cam follower - pushrod - rocker arm assembly.
The gas supply system was combined with the unit-injector on a spray-bomb. Ignition delay dependence on both gas conditions and injection parameters was studied. Turbulence level can be varied from low turbulence up to extreme turbulence at the start of injection. The pressure in the bomb prior to injection is as high as 16 MPa. This high pressure showed impact on the needle lift behavior.