Nuclear Burning Rates vs Temperature

What you are seeing: the energy generation rate $\varepsilon$ for the three dominant burning channels as a function of central temperature. The CNO cycle crosses over the pp chain near $T \sim 2 \times 10^7$ K.

Figure 1.

\varepsilon(T)

for pp, CNO, 3-α.

log10 T (K)7.20

ρ (g/cm³)100

WHAT TO TRY

Raise the central temperature past about 2e7 K: the CNO cycle (steep T^~17) overtakes the pp chain (T^~4). The dominant-channel readout flips and the curves cross.
Increase the density rho: the rates rise, since burning depends on the product of reactant densities, but the crossover temperature barely moves. Temperature sets which cycle wins.
Read the steepness: the CNO curve is far steeper than pp, which is why hot-core massive stars run on CNO and are sharply temperature-sensitive.