Nevada Wolf Pack Racing has been tasked with optimizing an engine to reach competitive levels of performance for the international Formula SAE Competition. SAE annually holds races across the world which test students’ abilities to design and build vehicles while following a strict set of regulations. Once inspection at the track is complete, schools from across the world will put their creations to the test, racing to prove who has the best engineering program. At Nevada, the responsibility of engine design has been given to five students in the senior design class with the goal of competing for the first time in Nevada’s history. Several changes will be made to a RM-Z450, 4-stroke engine to improve performance and meet competition standards. The main alterations that will be made to the engine are: creating a more efficient air delivery system within the constraints of competition rules, optimizing fuel consumption to meet both efficiency and power needs, converting the engine’s kick-start system to an electric start, and designing a cooling system that will effectively prevent excess heat buildup without overcooling the engine.
Our design concept focuses on the air flow through the intake system. In order to maximize the engine’s capabilities for torque and power output, it is necessary that the mass airflow rate be sufficient at high RPMs to combine with the amount of gasoline supplied by the fuel injector. Per the rules and regulations of the Formula SAE organization, a 20mm restrictor plate must be placed in the intake system in order to limit the amount of air that can be supplied to the engine. It is our objective to create an air delivery system that will be able to compensate for the air restrictor in order to recover and potentially exceed engine stock performance. The chosen method of overcoming the air restriction obstacle will be force air through a Venturi nozzle that is 20mm at its smallest diameter. This should help guide air flow through the restrictor in a way that will increase the velocity and ultimately recover air mass losses while minimizing turbulence and back pressure.
In order to test the proof of concept, we modified a wind tunnel, as shown above, to test for airflow using a Pitot probe under three different conditions. The three conditions of interest were airflow through the wind tunnel with openings of 38mm flat, 20mm flat, and a 20mm Venturi placed at the end of the wind tunnel. The 38mm flat simulated the stock engine intake diameter and provide baseline readings. This piece (light grey) was also used as a mounting surface for the next two test pieces. The 20mm flat piece (black disk) was used to test airflow through the required intake restrictor without any design or optimization. The Venturi attachment (black nozzle) was substituted in place of the 20mm orifice plate in the grey wind tunnel interface and was tested. All pressure readings were recorded using a data acquisition system to measure outputs from the Pitot probe.
Additional simulations were also conducted using Solidworks in order to simulate airflow and to visualize the resulting turbulence that can occur. An airflow simulation through the Venturi apparatus using Solidworks can be seen below.
In order to convert the engine’s kick start mechanism to an electric start, modifications needed to be applied to the kick start shaft directly. A decision was made to convert the starter by mounting a flywheel to the spline starting shaft. The intended mechanism will supply current to a recoil starter motor causing a rapid rotation of the flywheel simulating a kick activation response. This requires precise timing using a circuit time in order to ensure the flywheel does not over spin and cause damage to the engine housing and mechanism.
The air duct assembly was created to be attached to the sides of an existing vehicle for variable placement depending on customer needs. The box is designed to guide head wind into a chamber, forcing a constant atmospheric pressure due to the limited compressibility of air at subsonic velocities. With a constant pressure at the inlet and a vacuum created by the engine drawing in air every cycle, the pressure gradient will force air through the filter and hoses to the throttle body. The nature of this design sacrifices aerodynamics to an extent, but supplies the engine with sufficient air to draw from by maintaining the pressure drop for variable velocities.
The team decided to move from the stock carburetor design to an electronic fuel injection system in order to introduce precision by adjustment of fuel flow at inlet. The carburetor operates by the vacuum created as the air passes through the jets in the throttle body making fine tuning inaccurate and allowing for a high degree of variability in fuel injection rates should there be issues with air delivery. With the electronic fuel injection system monitoring the flow rate and oxygen content of intake air flow, regulated amounts of fuel can be injected using a high pressure fuel pump to force fuel in for specific amounts of time. Due to the restriction of air flow through restricting diameter, the listed functions of the system are important to ensure the engine runs at efficient and optimal conditions.
The 20mm diameter intake restrictor is required by Formula SAE rules and regulations in order to limit the engine capabilities of all schools equally. It is because of the restrictor attachment that the air duct and fuel injection design and selection were crucial. The restrictor design is important to function as well, thus, in order to maximize air flow capacity through the restricting diameter, a Venturi design was chosen. The Venturi will throttle down the air to the restricting diameter and will slowly increase to the cylinder inlet diameter at a low angle of attack in order to eliminate back flow which can slow air down due to turbulent streams.
The manufacturing process for this project required the group to divide efforts and focus on the different components. Due to the setbacks resulting from transit of our gear assembly for the starter a flywheel has been used.
The air box has been constructed from a high density foam. Due to the properties of this specialized material, it resulted in a labor intensive process that required hand tools to shape the air box in to the final product. Using scrap materials found in the shop from the rest of the team project, the prototype will be vacuum formed to produce the air box and attach the air filters.
The fuel injector we have selected comes with an Electronic Control Unit that comes with specialized software to control the rich and economical settings for maximum power or efficiency respectively. This required dedicated member attention in order to program the determined required values for air and fuel mixtures. This was an aftermarket product designed to be attached to smaller engine assemblies and was adapted for our engine by our team.
The part that required the most time machining to this point was the Venturi tube which was designed to recover the air losses due to the restricting diameter. The final composition was made from aluminum shaped to a 2inch outer diameter and turned on a lathe. The final product was smoothed to a polished finish in order to minimize air losses.
Orion Vazquez has grown up in Northwest Reno, Nevada since the age of 4. He is currently a Senior in Mechanical Engineering and is currently the President of the newly formed club Nevada Wolf Pack Racing. While working at LSP Specialty Products in Carson City, he has practiced skills learned at the University of Nevada, Reno and looks to continue his education in control system and robotics after graduating. When not studying, Orion likes to spend his time snowboarding, rock climbing and sleeping.
Stacey Estes was born in Seattle Washington, then spent most of her life in Arizona and California before attending University of Nevada, Reno. Driven by her passion for the intricacies and principals of classical mechanics. She decided to pursue Mechanical engineering. She is currently Senior status and will be graduating May of 2014. On her off days, she spends her time restoring her 1985 Z28 Camaro and enjoys outdoor recreational activities. She aspires to work with the Mythbusters television crew.
Jess Hayden is currently a Senior in Mechanical Engineering at University of Nevada, Reno with a focus on Unmanned Autonomous Systems. He has worked at Balance Point Home Performance for the past four years installing high efficiency Heating, Ventilation and Air Conditioning Systems.
Joe Thibedeau is a Senior in Mechanical Engineering, and has worked on several design projects throughout his college career. Working at ElectraTherm, Inc. as a Core Service Engineering Intern, Joe has further developed the skills and knowledge acquired in his engineering courses. In his free time, he likes off-roading, and dressing up in funny clothes to fight with swords.
Kris L. Geiser is a senior in Mechanical Engineering, and has held various construction jobs since the age of 12. Kris has furthered his college learning by working on the suspension system of his brother’s rock crawler, designing a snowboard and RC plane. In his free time he likes to snowboard and go explore the desert surrounding Reno and Carson.