Contents lists available at ScienceDirect Energy Conversion and Management journal homepage: www.elsevier.com/locate/enconman Development of rotary Wankel devices for hybrid automotive applications Ghada A. Sadiq a,b, ⁎ , Raya Al-Dadah b , Saad Mahmoud b a Mustansiriya University, Baghdad, Iraq b School of Engineering, University of Birmingham, Birmingham, UK ARTICLE INFO Keywords: Wankel compressor and expander CAES Thermal analysis Hybrid vehicles ABSTRACT Several attempts have been made to reduce greenhouse gas emissions (GHG) employing hybridization. Compressed air-electrical hybrid system is a promising technology which can be used to reduce the environ- mental impact of the automotive industry. In cities and urban areas, vehicle’s kinetic energy through braking can be converted to pressurized air which can be stored in a storage tank for reuse to operate the vehicle during starting, cruising, and acceleration. In this study, an efficient expander and compressor are developed using a Wankel device for the compressed air-electric hybrid vehicle. Volumetric Wankel rotary expander and com- pressor are essential devices for power generation in compressed air energy storage (CAES) system and com- pressed air hybrid engine powered by the braking energy system leading to a significant decrease in GHG emissions. Compared with conventional expanders and compressors, Wankel expander and compressor have significant advantages due to its compactness, lower vibration, noise, and cost. Different parametric studies have been carried out with different vehicle initial speeds (80, 60, 40) km/h and weights (500, 750, 1000) kg, various braking times (2, 3, 5, 7) s, and finally three different tank sizes (20, 35, 50) l using mathematical modelling MATLAB software. The maximum system energy-saving efficiency achieved was around 77% and instantaneous system efficiency of about 85% at an initial vehicle speed of 80 km/h, braking time of 3 s, and vehicle weight of 750 kg and compressed air tank of 35 l. 1. Introduction The automotive industry has seen rapid developments over the past decade to address global concerns regarding the high risk of air pollu- tion and decreasing fossil fuel recourses. Worldwide, the transportation sector consists of around 800 million passenger cars, which consume a significant amount of energy [1,2]. The primary power source of con- ventional vehicles is the internal combustion engine, which has a maximum efficiency of 45% for turbocharged direct injection (DI) diesel engines [2,3]. The vehicle’s kinetic energy wasted during braking can be recovered to reduce fuel consumption and CO2 emissions [1,2]. In 2010, the United State (US) Environmental Protection Agency (EPA) reported that there is an increase in the greenhouse gas (GHG) emis- sions from the human activity of (14% in the US and 26% in the world) since 1990. This increase leads to a rise in global earth temperature, which in turn results in many environmental disasters. Therefore, many scientific organisations recommended a significant reduction of 50% to 80% in GHG emissions below 1990 level by 2050 to prevent any risks to humans from climate change-related to a temperature increase of at least 2 °C. The study shows that 30% of GHG emissions in the United States are from the transportation sector, which is the second-largest source of GHG emissions. The majority of GHG emissions of transpor- tation come from light-duty vehicles, with a percentage of almost 60%. From 2009 to 2035, freight transportation GHG is expected to grow three times as fast as GHG from passenger vehicles [2,4]. Automobiles development with heat engines is one of the most significant achievements of modern technology. However, the auto- motive industry has developed rapidly, and a large number of vehicles in use around the world. Vehicles have caused and are still causing serious problems for society and human life. Degradation in air quality, global warming, and a reduction in oil resources are becoming sig- nificant threats to human beings. To control emissions and fuel con- sumption, development of clean, safe, and high-efficiency transporta- tion are stimulating interest in using hybrid technologies. It has been acknowledged that electric, hybrid electric, and fuel cell-powered drive train technologies are promising solutions to the problem of transpor- tation in the future [2,5]. Therefore, hybrid electric, electric battery, hydrogen, and compressed air vehicles are green environmentally friendly vehicles which are powered by alternative fuels and advanced technologies [2,6]. Pneumatic hybrid vehicles follow the same principle as hybrid electric ones. They operate two energy sources, fuel and compressed https://doi.org/10.1016/j.enconman.2019.112159 Received 24 June 2019; Received in revised form 7 October 2019; Accepted 8 October 2019 ⁎ Corresponding author. E-mail address: gadaabbas@uomustansiriyah.edu.iq (G.A. Sadiq). Energy Conversion and Management 202 (2019) 112159 0196-8904/ © 2019 Elsevier Ltd. All rights reserved. T