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Inside the flame

In the ascent engine, methane and oxygen swap partners at roughly 3,500 K, and the swap releases 802 kJ for every mole of methane.

See it in the tour: chapter how it survives, shot 7.5.

The engine

One ascent-vehicle launch burns 14.0 t of methane from the sea with 50.3 t of oxygen from the ice design. Pumps push both liquids into one chamber and the engine makes 221 kN design.

**Deep zoom: the engine.** The first rung of the zoom into a methane and oxygen engine.

The injector

The injector face sprays both liquids as fine streams that mix as they leave physics.

**Deep zoom: the injector.** Both liquids spray as fine streams that mix and begin to burn.

The flame front

The chamber holds the flame at roughly 3,500 K physics. The burn happens in a thin front where cold propellant becomes hot gas. Short-lived fragments of molecules, the radicals OH and CH, appear there physics. Excited CH glows near 431 nm, which is why the flame is blue-violet physics.

Bonds break and re-form

At the scale of a nanometre the burn is one equation:

CH₄ + 2 O₂ → CO₂ + 2 H₂O

Six bonds break, four C–H in methane and two O=O in the oxygen. Six bonds form, two C=O in carbon dioxide and four O–H in the water physics. The new bonds are stronger than the old ones, and the difference leaves as heat: 802.3 kJ per mole of methane burned physics.

**Deep zoom: bonds re-form.** The products of the reaction: one carbon dioxide and two water molecules, drawn as balls and sticks.

Deep zoom 1: methane burning illustrative

CH₄ + 2 O₂ → CO₂ + 2 H₂O

Products leave

energy released 802.3 kJ per mole of methane burned

Bonds broken: 4 C–H, 2 O=O. Bonds formed: 2 C=O, 4 O–H.

CH₄ + 2 O₂ → CO₂ + 2 H₂O. Stronger bonds form than break, releasing about 800 kJ per mole of methane. Hot, light molecules leave the nozzle at about 3.4 km/s.

10⁰ m The engine
10⁻¹ m Injector and chamber
10⁻³ m The flame front
10⁻⁹ m Bonds break and re-form

See it in the tour · The reaction lab

The card plays the same script as the tour. The flash is the moment of collision, the OH is the intermediate, and the energy bar fills as the products leave.

Deep zoom 1: methane burning: the products sit 802.3 kJ per mole lower than the reactants, so the reaction gives energy out. The hump between them is a barrier that the heat of the flame, a catalyst or a hot reactor lets the molecules climb. physics illustrative

Where the mass goes

A mole of methane and two of oxygen weigh 80.04 g before the burn and 80.04 g after. Chemistry loses mass too, but 802.3 kJ divided by the speed of light squared is 8.9 nanograms physics. No balance sees it. Fusion loses 0.4% of its fuel's mass physics, which is why it is a different kind of engine. See Fusion propulsion and helium-3.

What leaves the nozzle

Hot, light molecules, water and carbon dioxide, leave at about 3.4 km/s, a specific impulse of 345 s physics. The whole chain from sea and ice to this flame is in Methalox from Titan, and what the oxygen costs is in Fire on Titan.

Key numbers

Quantity	Value	Basis
Reaction	CH₄ + 2 O₂ → CO₂ + 2 H₂O	physics
Bonds broken / formed	6 / 6	physics
Energy released	802.3 kJ per mole of methane	physics
Flame temperature	about 3,500 K	physics
Mass converted per mole burned	8.9 ng	physics
Exhaust speed / specific impulse	about 3.4 km/s / 345 s	physics
Propellant per launch	14.0 t methane, 50.3 t oxygen	design
The reaction card	drawn from the DZ1 script	illustrative