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MAE 156B - Formula SAE Engine Dynamometer

A Senior Capstone Project

Spring 2018

Project Background:

Triton Racing is the UC San Diego's Formula SAE team circa 1997. The team designs, builds, tests and competes a Formula-style race car each year to compete at the end of the year in the Formula SAE Competition held in Lincoln, Nebraska. They want to continue producing cutting-edge race cars in order to perform better at the international competition. To do so, testing is a major priority and the first focus for the team is to measure and optimize engine performance. Presented as a MAE Department Capstone Senior Project and Triton Racing's solution, our team has taken on the task of completing the design and build of an engine dynamometer test bed for the Spring 2018 quarter. 

Project Objectives:

Figure 1: Power and torque data obtained for the 2016 Formula SAE vehicle via a professional engine dynamometer test run.

The objective of the team was to provide a package with the ability to the measure the revolutions per minute (RPM) of an engine along with the torque generated at the output shaft. Using those two measurements the torque and power output of the engine can be calculated. The second objective addressed needed to be the RPM range under which the system could operate, this definition would be determined by the RPM range of the engines that the system would be coupled to. Since the Formula SAE teams tend to use high performance motorcycle engines the system would be required to be able to perform a sweep of motor RPM from 3,000 to 16,000 RPM. An accuracy requirement was placed on both HP and Torque of +/- 0.5 horsepower and a repeatability tolerance of +/- 0.1 horsepower. Since the Formula SAE group operates within a compact space the physical system footprint also needed to be compact and portable to be able to move in and out of the project space for quick use and then storage thus the requirement was established to make the system self-contained.

Having been a capstone project started by a previous years group of students, the primary objective of this years team was to complete the assembly of the physical system and test and validate the performance of the system was a whole. The previous team managed to provide much of the physical system but still required validation of various subsystems and the overall system as a whole. The final goal is to provide data comparable to that of a previous professional dynamometer test that the Formula SAE team had (shown above).

Working Principle:

Figure 2: An exploded view of the water brake device used for the 2018 MAE-156B FSAE Engine Dynamometer.

An engine dynamometer measures power by using a measurement of the engine speed (RPM) and torque output and then multiplying the two together (along with a multiplication factor) to determine power output (typically in horsepower). The working principle is typically the same across the many types of dynamometers, but the method used to absorb the engine power output changes depending on the type of dynamometer used. For this project, a water brake type dynamometer was chosen for simplicity, cost, and ease of use. 

The water brake works as the absorption method in the system by transferring the energy from the internal shearing water to a stator which is then attached to a load cell at a specified distance from the revolution axis. Using the specified distance and the load measured by the load cell, a torque value can be calculated.  

Description of the Final Design:

Figure 3: The CAD assembly provided to the 2018 team by the previous year's team.

Figure 4: An isometric and section view of the CAD assembly.

The final solution for the engine dynamometer was built off of the previous team’s work. The team revised the design of components of various subsystems. The water reservoir system was revised to include a sealed lid and an access port to prevent leaking experienced during operation of the cooling system and engine. The final cooling system also incorporated revised routing for the driveline and a bypass valve to allow cooling of the internal seals of the water brake.

The fuel system was completed by integrating a fuel delivery system and storage unit onto the dynamometer. An FIA-FT3 approved fuel cell was sourced and chosen to be safe for this application. To support various different engines, a modular fuel delivery system was implemented. An external fuel pump was chosen with the ability to support fuel pressures up to 90 psi was chosen to be able to provide support for the requirement of various sized engines. Quick disconnects were included to have the ability to quickly remove an engine from the dynamometer instrument without needing to drain fuel from the delivery system.

In addition to the revisions to the fuel and cooling system, the team also added an electrical enclosure, a control station, a 12V electronic power supply system, and electronic control elements for the water brake inlet valve and throttle. The dynamometer now includes a NEMA rated electrical enclosure which houses the myRIO data acquisition system, the power 12V power supply, the control actuators, and the transistor-relay circuits for electronic control of the fans, battery contactor, water pump, and fuel pump via the LabVIEW UI. A Hi-tec HS785HB rotary servo and L16-R linear servo was integrated onto the water brake inlet valve and engine throttle to electronically control the load on the engine and the RPM of the engine being evaluated.

Summary of Performance Results:

TBD.

Executive Summary: Link