B. Alizadeh Kharkeshi - Faculty of Mechanical Engineering, Sea-Based Energy Research Group, Babol Noshirvani University of Technology, Babol, Iran
R. Shafaghat - Faculty of Mechanical Engineering, Sea-Based Energy Research Group, Babol Noshirvani University of Technology, Babol, Iran
S. Talesh Amiri - Faculty of Mechanical Engineering, Sea-Based Energy Research Group, Babol Noshirvani University of Technology, Babol, Iran
A. M. Tahan - Faculty of Mechanical Engineering, Sea-Based Energy Research Group, Babol Noshirvani University of Technology, Babol, Iran
A. Ardebilipour - Faculty of Mechanical Engineering, Sea-Based Energy Research Group, Babol Noshirvani University of Technology, Babol, Iran

In waste heat recovery from a heavy-duty diesel engine, with a focus on engine speed's impact, is explored. The critical problem of enhancing energy efficiency and reducing emissions through waste heat utilization is addressed. Waste heat in internal combustion engines, vital for sustainable energy use and environmental preservation, is investigated. Experimental analysis and thermodynamic modeling introduce Organic Rankine Cycle (ORC), Steam Rankine Cycle (SRC), and Combined Steam and Organic Rankine Cycle (CSO) for waste heat recovery. A non-linear relationship between engine speed and waste heat is identified.  Waste heat increases up to ۱۶۰۰ rpm and decreases thereafter. The CSO cycle outperforms ORC and SRC cycles, achieving ۴۳.۴% higher efficiency. Fuel energy savings demonstrate CSO's superior economy, along with excellence in Annual Carbon Dioxide Emissions Reduction (ACO۲ER). Waste heat recovery knowledge is advanced by introducing the efficient CSO cycle, contributing significantly to existing research.

experimental study, Fuel energy saving ratio, HD Diesel Engine, Waste heat recovery