Comparison of emissions and energy consumptions between a conventional diesel school bus and a plug-in hybrid school bus, emphasizes on recharging



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Quantifying the emissions due to the charging of the batteries of the plug-in hybrid electricity school bus operated by the Austin Independent School District (AISD) is the focus of this work. This plug-in hybrid school bus is one of only nineteen in the country, and was manufactured by IC Corporation. This hybrid school bus reduces fuel consumption and CO₂, NOx and PM emissions in comparison with conventional diesel buses. This reduction is good for the health of the children who take the school bus everyday as they are part of the population the most at risk because their lungs are still developing. In order to evaluate CO₂, NOx and PM emissions, measurements of the charging of the batteries versus time were taken for the two charging periods each day during the months of April and May 2009. These measurements were repeated in October 2009 when the route was changed for the new school year: 2009-2010. An analysis of the Austin electricity mix that provides electricity to the bus center was done hour by hour to evaluate the emissions, calculated on a g/mile basis. Measurements of the vehicle speed versus time and altitude were taken during February 2010 in order to explain some of the differences observed between the two routes. Different parameters were studied to analyze the results. The first parameter studied was the impact of the season on the emissions. The second parameter studied was the impact of the route and its characteristics (road length, traffic, grade, etc.). The last parameter studied was the difference between two methods used to evaluate the emissions using the electricity mix data. These two methods are different but each of them brings something to the analysis of the results.