Engineering >> Mechanical EngineeringOptimizing Engine Efficiency with the Rotational Inertia of a Flywheelby Gregory Klein
Submitted : Spring 2014
Back before utilities were commonplace rural farm communities had to use generators called hit and misses to power their homes and farm equipment. These generators unlike the generators of today would use a low horsepower engine to power a large flywheel. The idea behind the flywheel is that when it’s up to speed it carries with it a large amount of rotational momentum. Because of this the engine only has to work in intervals, once the rpm of the flywheel drops below a certain point the engine kicks in accelerating the flywheel back up to speed. Once the flywheel is back up to speed the engine then cuts off and the flywheel powers the alternator shaft as it decelerates. This use of rotational momentum makes these olden day generators much more efficient than todays as they use less fuel yet supply a comparable amount of energy.
The goal of this project is to take the ideas behind the old hit and miss engines and ap’ply them to today’s modern generators. This project will use the specs of an 8000 watt Brings and Stratton generator and apply them through physics and calculus in order to find the optimal flywheel radius necessary to maximize the total efficiency of the generator. For this project the acceleration and deceleration of the flywheel with and without the power of the engine will be calculated as a function of the change in radius of the flywheel. From this information 5 data points for both acceleration and deceleration are used to create two velocity equations were by the distance in radians can then be calculated. Through the use of the physical formula for work the total energy in joules done on the alternator for the 5 different data points can be found. By comparing this information to the energy output of the standard generator and the time the engine was under power, the percent efficiency’s for the 5 different radiuses are calculated. Through the use of optimization the optimal radius and efficiency is then also calculated. This came out to have a best possible radius of 41.5 cm and increased the efficiency of the generator by 196 %.
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