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Date of Award


Document Type

Campus Access Master's Thesis

Degree Name

Master of Science in Mechanical Engineering (MS)

Administrative Home Department

Department of Mechanical Engineering-Engineering Mechanics

Advisor 1

Mahdi Shahbakhti

Committee Member 1

David D. Wanless

Committee Member 2

Jeffrey D. Naber


More and more off-highway applications take advantage of hybridization using hydraulic or electric hybrid systems to increase the productivity and efficiency of the machines. The application of interest for this study is forklift that consists load cycle with intermittent peak load, which can provide the maximum benefits utilizing an optimum hybrid powertrain layout. In addition to this, there is also an interest to reduce tailpipe emissions or create a zero-emission solution due to strict emission regulations. Therefore, diesel engine performance and the after-treatment system are optimized in this thesis for a series hybrid forklift application in GT-Suite® simulation environment for fuel consumption benefits and emission reduction.

A GT-Suite® holistic modeling approach is utilized to establish a model-based hardware definition for an engine and after-treatment system that would accurately predict engine performance and emissions of the system. The developed engine model performance is validated with the experimentally verified IAV engine model data used for a similar application. The engine is optimized at a single operating point for optimal fuel consumption considering the performance of the after-treatment components. In addition, the effect of thermal management strategy like retarding injection timing and late post-injection of fuel during cold start is studied. The result shows tailpipe-NOx emission can be reduced by 40% by retarding the injection timing 15 CA deg. ATDC. Along with that, a series hybrid powertrain is designed to represent the series hybrid forklift architect with a heuristic-based controller that defines different modes of operation. The developed hybrid powertrain system can meet the performance requirement for 20% gradeability.

The energy utilization for a developed series hybrid forklift in VDI 2198 cycle is mainly used for the vehicle rolling resistance as the vehicle mass including the rated load is high equivalent to 5.90 kW-hr. The energy required to overcome drag is only 0.01 kW-hr due to low vehicle speed in the cycle. The fuel consumption of conventional forklift is compared with a developed series hybrid forklift for the 60 VDI 2198 cycles, which shows reasonable fuel saving. The result shows optimally designed hybrid electric forklift can minimize fuel consumption by 20%. Furthermore, the cost of after-treatment components can be reduced by 19.7% using smaller catalyst volume for a single point operating diesel engine