Using thermoelectric generator (TEG) for waste heat recovery on internal combustion engines is a promising solution for efficiency improvement. This study investigates the behavior of TEG during engine operation. It distinguishes the effect of the engine flow properties on the TEG performance. Three test rigs have been designed and built to investigate this effect. The results confirm that there are two main engine exhaust gas properties that affect the TEG performance, namely: engine exhaust gas composition and engine exhaust gas pulsation. An analytical model has been developed to identify and quantify the effect of each parameter on the convective heat transfer coefficient between the exhaust gas and the thermoelectric module, hence on the TEG performance. Test results show a difference in the TEG output power up to 30% between hot air and real engine test at perfectly similar TEG inlet temperature and mass flow rate. The model identifies that 5-12% of this difference is related to the gas composition whereas another test rig proves that the engine exhaust pulsating flow is responsible for the remaining difference (88-95%). Further studies will be conducted to improve the TEG design thanks to this pulsation effect behavior. (C) 2018 Elsevier Ltd. All rights reserved.