🔥 Rocket Engine — de Laval Nozzle

Explore how a de Laval nozzle converts hot, high-pressure combustion gases into supersonic exhaust, generating thrust. Adjust chamber pressure, nozzle area ratio, and propellant combination to see how each affects exit velocity, thrust, and specific impulse.

Propellant

Propellant combination

Chamber & Nozzle

Chamber pressure (MPa) 5.0 MPa Throat area (cm²) 50 cm² Area ratio ε = A_e/A_t 25 Ambient pressure (kPa) 101 kPa

Performance

Thrust—

Isp (vacuum)—

Isp (ambient)—

Exit velocity—

Exit pressure—

Mass flow—

Expansion—

Key equations:
c* = √(γRT_c/γ)/(Γ) — char. vel.
v_e = √(2γ/(γ-1)·RT_c·[1−(p_e/p_c)^((γ-1)/γ)])
F = ṁ·v_e + (p_e − p_a)·A_e
Isp = F / (ṁ·g₀)

How the de Laval Nozzle Works

The de Laval nozzle (converging-diverging nozzle) is the key component that converts thermal energy from combustion into directed kinetic energy. In the converging section, subsonic hot gas accelerates. At the throat — the narrowest point — flow reaches exactly Mach 1 (sonic conditions). In the diverging section, the flow becomes supersonic and continues to accelerate. The area ratio ε = A_e/A_t determines the exit Mach number and exit pressure. Optimal expansion (p_e = p_a) maximizes thrust for a given altitude. Underexpanded (p_e > p_a) and overexpanded (p_e < p_a) nozzles lose efficiency. High chamber pressure enables smaller throat area for the same thrust, reducing engine mass.