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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.