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Overall view of the "plumbing" on the forward end of the Ascent Propulsion System engine.

Picture 5 of 8.

The larger diameter duct at left the fuel supply line and the smaller-diameter duct at right is the oxidizer supply.

Note the bulbous reservoir at the end of the fuel duct. During engine development, the engine suffered from hard starts; it was discovered that this could be solved by admitting the oxidizer into the combustion chamber before the fuel. Rather than changing the timing on the valves or otherwise modifying the engine start sequence, engineers added this reservoir to the end of the fuel duct, delaying the fuel's entrance into the combustion chamber.