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

Picture 2 of 8.

The smaller-diameter duct in front is the oxidizer supply line and the larger diameter duct in the rear is the fuel 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.