ANALYSIS OF COMBUSTION CHARACTERISTICS AND TAILPIPE EMISSIONS OF SPARK-IGNITION ENGINES DURING THE THREE-WAY CATALYST WARM-UP PHASE

Emissions management in hybrid-electric vehicles can be particularly critical. This is due to the drop of exhaust temperature during the shut-off phases of the thermal engine, which can lead the aftertreatment system to fall below its activation temperature. Traditionally, spark-ignition engines have induced this activation by using late spark timings so that the end of combustion occurs close to the exhaust valve opening. However, this has a negative impact on engine thermal and combustion efficiencies (and therefore carbon dioxide emissions). In this paper, the impact of warm-up calibration on combustion and emissions management is analyzed. For this purpose, a fully instrumented 1.3-liter gasoline direct injection engine was tested for different spark calibration and ambient temperature conditions. The speed and load were controlled to represent similar conditions to those achieved in the first stages of a certification cycle. Emissions measurements were performed before and after the three-way catalyst to evaluate its activation. The results show that moderate spark timings are preferable at standard room temperature (25 degrees C), while at cold ambient conditions the best results are found with more aggressive spark timings.