Two-Stroke Exhaust System Design

From Mindworks
Jump to: navigation, search
Team Name Two Stroke Smoke
Duration Fall 2017 - Spring 2018
Faculty Advisors Dr. Dan Cordon
Team
  • Cade Smith
  • Jason Maas
  • Phoenix Duncan
  • Zachary Lipple

The goal of this project is to design an exhaust system that will reduce the noise and emissions of a two-stroke snowmobile, without significantly sacrificing power. The system will include a tuned pipe, catalytic converter, muffler, and a controllable backpressure valve. We must have a fully manufactured and tested system before the Clean Snowmobile Competition, held in March. Testing data will be presented in the UICSC team's technical paper and design presentation.


Problem Definition

Background

Since 2001, students from the University of Idaho have competed in the SAE Clean Snowmobile Challenge. The competition is allows college students to work on reducing the noise and pollutant emissions while increasing the fuel economy of stock snowmobiles. This year, the UI CSC senior design team will be re-designing the entire exhaust system on the snowmobile.

Specifications

Technologies Used
Title Image Description
Tuned Pipe
2017 two-stroke-smoke tuned-pipe.gif
A tuned pipe utilizes pressure waves to reduce the impacts of short-circuited fuels on the two-stroke platform. The tuned pipe is designed to work most effectively over a specified rpm band. Since the engine of the 2018 snowmobile was detuned to meet competition power requirements, the existing tuned pipe needs to be modified.
Back-pressure Control Valve
2017 two-stroke-smoke exhaust-baffle.png
Two stroke engines are heavily affected by intake and exhaust pressure levels. A valve was added to the exhaust stream of the snowmobile to increase back-pressure at low engine speeds and loads in order to increase engine efficiency and performance.
Catalytic Converter
2017 two-stroke-smoke catalytic-converter.gif
A three-way catalytic converter was added to the exhaust stream to reduce CO, UHC, and NOx emissions. Because the catalytic converter drastically increases exhaust stream temperatures, it may be prudent to place it at the exit of the muffler to improve muffler life.
Muffler
2017 two-stroke-smoke muffler.jpg
A custom muffler was designed and manufactured by the Two-Stroke Smoke team to reduce the sound output of the snowmobile. Multiple models were simulated for pressure and sound reduction estimates, and the best of the models was manufactured and added to the competition snowmobile.

Deliverables

  • An exhaust system that can be used by the UICSC team for the next four years
  • Sound level and flow simulations for the muffler.
  • A GT Power model for the engine and tuned pipe
  • Heat transfer and flow simulations for the catalyst and muffler
  • Documentation of control system and manufacturing plans

Design Components

Tuned Pipe

Image Description
2017 two-stroke-smoke StockPowerSweep.png Since the tuned pipe operates most efficiently over a specific band of engine speeds, we need to modify ours to match our reduced-speed engine. The first step in this process was to run a power sweep on the dynamometer to determine what the engine's peak rpm would be. A stock 850 E-TEC power sweep recorded by the Two-Stroke Smoke team is shown to the left.
175px The next step was to create a model in GT Suite that would optimize tuned pipe length for a given engine operating range. To do this we had to measure and create math models to describe the exhaust ports, intake ports, RAVE valves, and air intake. The math models were created in Matlab.
2017 two-stroke-smoke PipePackaging.png Once we knew the optimal length of the tuned pipe, we needed to weld extension pieces into the header and dwell sections of the tuned pipe to reach that length. We used a laser scanner to create an open volume that matches the inside of the snowmobile in SolidWorks, then modeled a few tuned pipes of the correct length until we found one that would fit in our chassis.
175px We then modified the tuned pipe and tested it against the stock tuned pipe on the dynamometer. As can be seen in the plot on the left, we saw a ___ increase in ___ and a ___ increase in ___.

Muffler

Image Description
2017 two-stroke-smoke AM2.jpg Since a muffler was created last year by the UICSC team that passed the sound event at competition, we decided to follow their design ideas. We kept the same basic principles, but modified the muffler slightly to reduce back-pressure in order to accommodate the exhaust baffle. We also needed to make our muffler more durable, so we talked with sponsors and obtained sound materials that would stand up to higher temperatures.
2017 two-stroke-smoke MufflerModsChart.jpg The chart to the left (click to expand) shows the simulated back-pressure decrease that modifications made to the original muffler. However, a decrease in back-pressure almost always leads to an increase in sound emissions.
175px To verify that our muffler would be as quiet at the 2017 muffler, we ran two separate sound tests. First we ran it on the UI Sound Box, an anechoic sound box from which we can determine the sound transmission levels of different sound materials, expansion chambers, and mufflers across a range of frequencies. We also ran a J1161 sound test on the 2018 chassis with the 2018 muffler, and compared sound pressure readings to the 2017 chassis with the 2017 muffler, which we know passed the sound event at the previous competition.
175px The plot on the left shows the results from the sound box. It shows that at most frequencies we ... We also saw a ___ reading on the J1161, compared to the 2017 configuration.

Exhaust Baffle

Image Description
175px The exhaust baffle components were designed and machined in-house.
175px We decided to start the exhaust baffle with a simple control scheme. Based on engine speed and throttle position, the baffle would be set to one of three or four positions, more open at high engine speeds and loads, and more restricted at lower engine speeds and idle. Testing to pick positions and create a map were done on the dynamometer in the Small Engine Research Facility.
175px

Catalytic Converter

Image Description
175px In testing with a pre-muffler catalytic converter, exhaust temperatures were getting high enough to melt sound material and weaken the metal in the muffler. Since this system needs to last for at least four years, it was decided that we would instead utilize a pre- and a post-muffler catalyst. The pre-muffler catalyst is a smaller diameter catalyst with a less dense monolith and a lighter coating. It's main purpose is to light off quickly and keep exhaust temperatures high enough to light off the post-muffler catalyst. The post-muffler catalyst is a larger, more dense, and more heavily coated catalyst. It does most of the emissions conversion in the system and is integrated into the outlet of the muffler.

Testing Results

Team Information

Picture Bio Discipline
2017 two-stroke-smoke Cade.jpg Cade Smith: Cade is a senior studying mechanical engineering. His focuses are in engine development, combustion, and manufacturing. His hobbies include camping, hiking, and playing guitar. Mechanical Engineering
2017 two-stroke-smoke Jason.jpg Jason Maas: Jason is a senior studying mechanical engineering. His focuses are in numerical methods, robotics, and FEA. His hobbies include camping, hiking, and playing guitar. Mechanical Engineering
2017 two-stroke-smoke Phoenix.jpg Phoenix Duncan: Phoenix is a senior studying mechanical engineering. His focuses are in... Mechanical Engineering
2017 two-stroke-smoke Buttons.jpg Zachary Lipple: Zachary is a senior studying mechanical engineering. His focuses are in... Mechanical Engineering

Document Archive

Other Documents Return to Contents