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In this paper we present the results of full-scale chassis dynamometer testing of two hybrid transit bus configurations, parallel and series and, in addition, quantify the impact of air conditioning. We also study the impact of using an electrically controlled cooling fan. The main trend that is noted, and perhaps expected, is that a significant fuel penalty is encountered during operation with air conditioning, ranging from 17-27% for the four buses considered. The testing shows that the series hybrid architecture is more efficient than the parallel hybrid in improving fuel economy during urban, low speed stop and go transit bus applications. In addition, smart cooling systems, such as the electrically controlled cooling fan can show a fuel economy benefit especially during high AC (or other increased engine load) conditions.

A Benchtop Engine System (BES) is described to evaluate the NOx emission characteristics of diesel fuels. The BES enables the efficient testing of the combustion and NOx emission features of alternative fuels and additives. The BES comprises a computer controlled single cylinder engine generator, fuel blending and feed system, and NOx analyzer. The engine can be operated at different loads using the programmable load control. NOx concentration are monitored and recorded to evaluate the impact of the diesel fuel and/or additive. Several commercial diesel fuels and one commercial fuel additive were tested in both the 500 HP Heavy Duty Chassis Dynamometer and the BES. The reported results demonstrate the BES capabilities, differences in the NOx emission features of several fuels and additives.