Praveen, V. and Sethupathi, P., "Active Muffler for Single Cylinder Engine, Using Electronic Throttle Control for Formula Student Cars," SAE Technical Paper 2017-28-1935, 2017.
Formula SAE is a prestigious engineering design competition, where student team design, fabricate and test their formula style race car, with the guidelines of the FSAE rulebook, according to which the car is designed, for example the engine must be a four-stroke, Otto-cycle piston engine with a displacement no greater than 710cc.According to FSAE 2017 Rule Book , ARTICLE 3, IC3.2 and IC3.3 state that the maximum sound level should not exceed 110 dBC at an average piston speed of 15:25 m/s (for the KTM 390 engine, which has 60 mm stroke length, the noise level will be measured at 7500 RPM) and 103 dBC at Idle RPM. So, the active muffler which works as a normal reflective muffler till the 7500 RPM range, after which an electronic controlled throttle mechanism is used to reduce the backpressure (since after 7500 RPM the noise level doesn't matter in FSAE) by using tach signal from the engine to control the throttle (two position). The electronic throttle will be controlled using an ardino board and control the backpressure, with respect to the Engine RPM. This ensures that Noise level rules are met without compromising on the performance of the engine.Further research is required in utilizing the active throttle setup for continuously variable position (with respect to the RPM), in order to tune the exhaust system according to individual requirements and for achieving the required acoustic tuning of the exhaust system.