# Design of a Mass Air Flow Sensor Employing Additive Manufacturing and Standard Airfoil Geometry
## 1 Introduction  
Marine industry employs a wide range of internal combustion (IC) engines for various applications; while their role as the prime mover of a vessel is undoubtedly the most important, it is broadly accepted that IC engines have a fundamental role in ship operations in general, making their proper operation crucial; for example, a typical Ro-Ro vessel has four medium power 4-stroke engines installed onboard, which are required for the operation of the corresponding generator-sets [1]; a possible failure even only at one of the installed IC engines will immediately result in a safety compromise, according to the corresponding safety regulations [2], with severe consequences. Mass Air Flow (MAF) sensors are measuring devices integrated to IC engines. Their role is to measure the air intake during the operation of the engine in order to consequently efficiently adjust the amount of fuel supplied during combustion. The majority of the MAF sensors currently employed are thermal flow microsensors, since, during the last two decades, microsystem technologies have greatly contributed to the reduction of the cost for this specific type of sensor [3, 4]. Printed Circuit Board (PCB) technology is a new sensor fabrication technology that combines printed circuit and MEMS technology and addresses some drawbacks of the standard microelectronic fabrication process [5]. Briefly, the sensing elements of a sensor developed with PCB technology are inherently connected to the macroworld, overcoming the necessity for performing wire bonding (a delicate process for the creation of the necessary electrical pathways between microscale sensing elements and the corresponding macroworld circuitry), with immediate benefits in device complexity, mechanical reliability, process time, and cost [5, 6]. Airfoils find many applications in the industry, including, but not limited to, aeronautics, naval, and automotive engineering. An airfoil is a streamlined body, capable of generating significantly more lift than drag, which provides much smoother flow than non-streamlined bodies, keeping airflow attached to the surface rather than breaking free and causing turbulence. Numerous airfoils can be designed for different applications [7]. The most renown are the NACA series developed by the National Advisory Committee for Aeronautics airfoils during the late 1920s and into the 1930s [8; 9]. In this paper, we present a novel air intake sensor, which is based on additive manufacturing and PCB technology. In more detail, the sensor's sensing element was fabricated, utilizing only standard PCB fabrication techniques and commercially available sensing components, while 3D printing technology was employed for fabricating an appropriate air flow, shaping housing. The housing's geometry was derived through appropriate Computational Fluid Dynamic (CFD) simulations-in order to investigate the effect of the main design parameters, employing SimScale Online CAE Simulation Platform [10]. The contribution of additive manufacturing is of paramount importance, as it significantly minimizes the design constrains during manufacturing [11], allowing implementation of the derived topology as per the optimum deduced from CFD simulations. As a general remark, the obtained optimal geometry efficiently addresses the measuring challenges present on the intake flow of an IC engine; it is originated in a flow-bypass topology studied in previous work [12] combined with standard airfoil geometry; the airfoil geometry implementation drastically improves the bypass flow profile compared to a previous study [12].