Reducing cold-start emission from internal combustion engines by means of a catalytic converter embedded in a phase-change material

Abstract

Under normal operating conditions, catalytic converters appear to be the most effective means of reducing air pollution from internal combustion (IC) engines. The conversion efficiency, however, declines very steeply for temperatures below about 350°C and is practically zero during the starting and warming-up period. Improving the conversion efficiency under these conditions is important, particularly in large cities, where the number of startings per vehicle per day tends to be high. Among the more successful solutions are preheating of the catalyst electrically, warming up of the catalyst in an external combustion chamber, installation of an auxiliary small-capacity catalytic converter, and employment of an adsorbing unit between two catalysts. Although these methods are quite effective, their disadvantage lies in the fact that they require an external energy source, an additional component (a control unit) or a three-stage catalyst. In the present work an investigation was made of a solution based on the exploitation of thermal capacitance to keep the catalyst temperature high during off-operation periods. A phase-change material (PCM) with a transition temperature of 352.7°C, which is slightly above the light-off temperature of the metallic catalyst, was specially formulated, and a system comprising a catalytic converter embedded in the PCM was designed and tested. Under normal engine operating conditions, some of the thermal energy of the exhaust gases was stored in the PCM. During the time that the vehicle was not in use, the PCM underwent partial solidification, and the latent heat thus produced was exploited to maintain the catalyst temperature within the desired temperature range for maximum conversion efficiency.

Technical note: Use of an atmospheric simulation chamber to investigate the effect of different engine conditions on unregulated VOC-IVOC diesel exhaust emissions

“…The SpVOC-IVOC emission rate was lower in the WIFL experiment than observed in the cold-loaded experiment, where a higher engine temperature was measured upon injection. The HC removal efficiency of the DOC below 200 • C is close to zero (Korin et al, 1999;Roberts et al, 2014;Majewski and Khair, 2006;Russell and Epling, 2011), suggesting the lower SpVOC-IVOC emission rate observed in the WIFL experiment is the result of increased combustion efficiency from the higher engine speed and load applied before idling conditions. Engine "warm-up" increases the temperature of the lubricant, coolant, and engine components, reducing friction and increasing combustion efficiency, thus resulting in less unburnt fuel emissions in the exhaust gas (cf.…”

“…The DOC HC removal efficiency is strongly dependant on working temperature. Below 200 • C the DOC HC removal efficiency is close to 0 %, rising sharply to near 100 % HC removal efficiency at ∼ 430 • C (Korin et al, 1999; Roberts et al, Figure 5. Comparison of measured VOC-IVOC emission rates in replicate warm high-load experiments 1 and 2 (exps.…”

“…The results from this study show that at low engine loads and speeds, the emission rates of unregulated VOC-IVOCs per kilogram of fuel burnt are considerably greater than emitted at higher engine speeds and loads (emission rates were 65 times greater from a coldstart than at maximum applied engine speed and load). Furthermore, it was found that the exhaust gas composition varied with combustion efficiency and DOC HC removal efficiency, both which are strongly dependent on working temperature (Korin et al, 1999;Roberts et al, 2014;Majewski and Khair, 2006;Russell and Epling, 2011). The effect of combustion efficiency on the exhaust gas composition was observed at engine temperatures below ∼ 150 • C (below the working temperature of the DOC) and at the maximum applied engine speed and load (700 • C), where combustion efficiency dominated over the effect of the DOC on the exhaust gas composition.…”

Gold, an alternative to platinum group metals in automobile catalytic converters

“…The conversion efficiency of commercial catalytic converters declines very steeply at temperatures below 350°C and is practically zero during the starting and warming-up periods [37]. These cold-start emissions impose a serious pollution problem and require the identification of new catalysts that can operate at low temperatures to achieve their abatement [38].…”

Artificial neural network based modeling of heated catalytic converter performance

“…These techniques are referred to as fast light-off techniques. Among the more successful methods that have been developed for shortening the light-off time are locating of the converter closer to the exhaust manifold, secondary air injection, electrically and burner heated catalysts [1,4,7,[10][11][12][13][14][15][16].…”