Diesel Cycle: Compression-Ignition Engine Simulator

Engine Parameters

Compression ratio r 18.0

Cutoff ratio r_c (injection duration) 2.20

Intake temperature T₁ 300 K

Engine speed 900 rpm

Cycle Phase

Compression (1→2)

Live Readouts

Thermal efficiency

Peak pressure P₃

0 bar

Peak temperature T₃

0 K

How it works

The air-standard Diesel cycle models a compression-ignition engine with four idealised strokes on a fixed mass of air (γ = 1.4):

1→2  Isentropic compression   (r = V1/V2)
2→3  Constant-pressure heat addition (fuel injection, rc = V3/V2)
3→4  Isentropic expansion     (power stroke, V4 = V1)
4→1  Constant-volume heat rejection (exhaust)

Unlike the Otto cycle, heat is added at constant pressure — the piston keeps moving down while fuel injects, which is why the cutoff ratio r_c (not a spark timing) sets how much of the power stroke is spent adding heat instead of expanding freely.

T2 = T1·r^(γ-1)          P2 = P1·r^γ
T3 = T2·rc                P3 = P2  (constant P)
T4 = T3·(rc/r)^(γ-1)

η = 1 − (1/γ)·(rc^γ − 1) / [r^(γ-1)·(rc − 1)]

Compression ratio r — higher r raises T2 above the fuel's autoignition point (that's what lets Diesel engines skip a spark plug) and raises efficiency.
Cutoff ratio r_c — more injected fuel means a longer constant-pressure segment, which raises peak temperature and torque but lowers efficiency, since heat added at constant pressure does less work than heat added at constant volume (why Diesel efficiency trails an equal-r Otto cycle).
The piston/crank/rod animation is driven directly by slider-crank kinematics, and the highlighted P–V loop segment always matches the physical stroke you're watching.

P–V diagram

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