Coagulation of combustion-generated particles has been investigated in low and intermediate temperature regimes in a tubular reactor with a residence time of 1.65s. Particles, generated by premixed ethylene/air flames with equivalence ratios above the soot threshold limit, are fed to a tubular reactor, which can be operated at temperatures up to 650K. A wide range of equivalence ratios are used to generate particles with different characteristics. The evolution of the particle size distributions has been evaluated by a differential mobility analyzer with high sensitivity in the 2–100nm size range. The effect of the reactor temperature on coagulation has been systematically studied. Particles exhibit different coagulation efficiencies at the different temperatures. At room temperature, 2–4nm particles fed to the reactor coagulate forming particles as large as 10–20nm, whereas at higher temperatures the size distribution of the particles does not change with respect to that measured at the inlet of the reactor. This behavior suggests a very ineffective coagulation efficiency at higher temperatures for small nanoparticles. Larger particles do not exhibit this high sensitivity to temperature, substantially maintaining very high coagulation efficiencies. These considerations have been confirmed by numerical simulations conducted both with constant and size-dependent coagulation efficiency. The numerical results confirm that also at low and intermediate temperature regimes, the use of a size-dependent coagulation efficiency is mandatory to match the evolution of the particles during coagulation. On the other hand, the simple model of coagulation based on the van der Waals interactions between particles in the framework of gas kinetic collision theory is in slightly disagreement with the experimental results for very small particles, suggesting that more advanced modeling based on quantum mechanism and molecular dynamics are necessary to correctly reproduce the experimental data.