Experimental study for the effect of hot-film air mass sensor contamination on engine performance

The hot-film air mass (HFM) sensor is essential for accurate engine control. Contamination of the sensing surface can introduce measurement bias, thereby affecting control strategies, combustion behavior, and emission performance. In this study, controlled exhaust-induced contamination experiments were conducted to investigate HFM degradation characteristics and to quantify the consequent impacts on engine control responses, performance, combustion, and emissions. The HFM was exposed to engine exhaust gas for 2–10 min under fixed operating conditions to simulate different contamination levels. Three representative operating points were selected to evaluate engine responses: A (1692 r/min, intake airflow about 120.76 kg/h), B (2201 r/min, intake airflow about 225.9 kg/h), and C (2710 r/min, intake airflow about 342.92 kg/h). When the intake flow exceeds 100 kg/h, contamination significantly lengthens the HFM signal period, leading to an underestimation of intake airflow, with nonlinear deviation becoming more pronounced at higher flow rates. After 10 min of contamination, the maximum underestimation reaches 12.35% at an intake airflow rate of 500 kg/h. This bias induces substantial control adjustments. Under the medium (B) and low (A) load conditions, when the indicated airflow decreases by 10%, the EGR (Exhaust Gas Recirculation) rate drops sharply by 61.22% and 83.68%, respectively, while the actual intake airflow increases by 13.17% and 8.89%, accompanied by increases in VNT (Variable Nozzle Turbocharger) nozzle opening of 47.44% and 11.93%. Under the high-load condition (C), with the EGR valve closed, the smoke-limiting constraint reduces cycle fuel injection quantity by 7.37%. Although BSFC (Brake Specific Fuel Consumption) decreases slightly (3.60%, 1.85%, and 0.48% for A-C), high-load torque decreases by 6.64%, a 3-4 times greater deterioration than at lower loads. Combustion degradation is observed at high load, with the combustion centroid (CA50) delayed by 1.77°CA. In terms of emissions, CO, soot, and THC decrease, whereas NOx increases markedly by 119.06% and 75.77% under the low- and medium-load conditions, respectively. These results quantify the contamination-induced sensor bias and its propagation through engine control to combustion and emission outcomes, providing experimental support for HFM diagnostics and emission-control strategy development.