Date of Graduation

2001

Document Type

Thesis

Degree Type

MS

Committee Chair

Nigel N. Clark

Abstract

Recent chassis and on-road testing of hybrid electric buses (HEBs) performed by West Virginia University demonstrated the potential of hybrid technology to be significantly fuel efficient and reduce regulated emissions and greenhouse gas output compared to buses with conventional drivetrains. All heavy-duty engines, including the engines in HEBs, need to be certified through the Federal Testing Procedure (FTP) prescribed by the United States Environmental Protection Agency. The operation of series HEBs with engine-generator units does not follow the behavior of the FTP, which is transient in nature. It was evident that, unlike conventional buses, HEBs were designed to operate over a limited range of the engine’s torque curve to ensure high engine efficiency. In the case of series hybrid electric vehicles (HEVs), additional power is supplied by energy stored in batteries through a motor-generator when necessary. This study presents evidence for a need of an alternative engine certification procedure specifically written for these new buses. Such a procedure must focus on the testing of the hybrid bus engine on cycles that are representative of their engine speed and engine torque operating range. In-use series hybrid electric bus engine torque and speed envelopes were analyzed and compared to conventional bus engine operation and the FTP certification cycle. From these results, it was evident that hybrid bus engines operated with substantially less aggressive transient behavior than were obtained by following the FTP. Since aggressive engine operation contributes directly to an increased formation of particulate matter and carbon monoxide (CO) in diesel engines, actual emissions from in-use hybrid electric bus engines are better represented when operating the engine on steady state cycles. Thus new duty cycles must be designed to meet standards of the hybrid bus’ life operation.

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