Assessment of exhaust raw emissions and aftertreatment performance in a retrofitted heavy duty-spark ignition engine operating with liquefied petroleum gas

Abstract

This study investigates the effects of varying Liquefied Petroleum Gas compositions on pollutant emissions and three-way catalyst performance in retrofitted heavy-duty spark-ignition engines. It focuses on fuels with varying propane and butane ratios, providing new insights into the influence of the composition of Liquefied Petroleum Gas on catalyst activity and tailpipe emissions. Representative conditions from the world Harmonized Transient Cycle were selected to comprehensively assess engine emissions and catalyst performance. Experiments under constant and variable λ conditions tested the catalyst's response concerning raw emissions, exhaust temperature, and space velocity, all variables affected by engine operation. Key findings indicate that catalyst performance is not significantly affected by Liquefied Petroleum Gas composition. Under constant λ conditions, the catalyst achieved high conversion efficiency of carbon monoxide, unburned hydrocarbons, and nitrogen oxides, especially under rich conditions (λ = 0.990). However, rich conditions can lead to elevated ammonia levels, although nitrous oxide generation remains low in all circumstances. Implementing λ pulse strategies reduced ammonia formation to around 25 mg/kWh, ensuring high catalyst conversion efficiency for all pollutant species after optimizing the amplitude and frequency of the pulses to establish the balance of reducing-oxidizing species and oxygen storage for each operation mode. Crucially, Liquefied Petroleum Gas composition was determined to be non-critical for the catalyst in these engines, promoting the use of this fuel in retrofitted engines and promoting for a shift towards cleaner transportation.