The hybrid powertrain with an advanced three-way catalyst (TWC) can contribute to the decarbonization of current gasoline engine-powered vehicles. Compact TWCs are used in next-generation hybrid electric vehicles (HEVs) to make room for a bigger battery. However, performances of a compact TWC deteriorate under dynamic excess air ratio (lambda ). Lambda perturbation (dithering or rich-lean cycling) is a technique to improve transient TWC performance. The TWC conversion rate under dynamic lambda perturbation has not been well understood in real engine experiments. This work experimentally investigates the impact of lambda perturbation (frequency f and amplitude A) using an actual engine test. The experiments are performed using a mass-production 4-cylinder, 2.4 L gasoline engine equipped with a modified TWC reactor. THC, CO, and NO conversion rates are investigated under f = 0–1.0 Hz, A = 0–0.1, and exhaust gas temperatures T = 270–350°C. The results show that NO, THC, and CO conversion rates are low for T = 270°C for all frequencies and amplitudes. NO conversion rate is improved at A ≥ 0.04 under various f and T. THC conversion rate over 80% can be obtained under T = 350°C, while CO conversion rate is nearly 100% at T = 350°C for A = 0.02–0.08 and all frequencies. The impact of frequency and amplitude on the oxidation reaction rate of CO, NO, and THC are also discussed.
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