بهینه‌سازی انباره موتور احتراقی یک چمن‌زن دوشی جهت کاهش سطح آلایندگی صوتی

در مطالعه حاضر امکان بهینه‌سازی انباره یک موتور احتراقی کوچک مربوط به چمن‌زن دوشی جهت کاهش سطح سروصدای تولیدی آن مورد بررسی و ارزیابی قرار گرفت. آزمایش‌ها به‌صورت فاکتوریل، بر پایه طرح کاملاً تصادفی و در سه تکرار انجام گرفت. تیمارهای پژوهش عبارت بودند از: انباره اصلی موتور و انباره بهینه‌شده در دو سطح 3000 و 5000 دور در دقیقه و عوامل تحت مطالعه شامل تراز فشار صوتی (spl) و تغییرات فشار پس‌زنی (pδ) در حالت بدون بار. به‌علاوه تحلیل فرکانسی تیمارها برای بررسی عملکرد صوت‌های خروجی موتور مورد بررسی و تحلیل قرار گرفتند. جمع‌آوری داده‌های صوتی طبق ویژگی‌های مکان آزمون بر اساس استاندارد موسسه استاندارد و تحقیقات صنعتی ایران که درخصوص مقررات آزمون برای اندازه‌گیری سروصدای انواع چمن‌زن‌ها است، انتخاب شد. طبق نتایج به‌دست آمده، در دور 3000 دور در دقیقه، تراز فشار صوت انباره بهینه شده به‌میزان 6.4% نسبت به انباره اصلی کاهش پیدا کرد. همچنین نتایج حاصل از تبدیل سریع فوریه (fft) نشان داد که شدت و دامنه فرکانس‌های خروجی از انباره بهینه شده در محدوده فرکانس‌های 10 تا 15کیلو هرتز کاهش پیدا کرده است. به‌عنوان نتیجه کلی حاصل از تحقیق حاضر، با نصب انباره بهینه شده میزان حداکثر ساعت کاری کاربر بر اساس استاندارد موسسه استاندارد و تحقیقات صنعتی ایران حدود مواجهه در مقابل صوت حاصل از موتور، در دور 5000 دور در دقیقه برابر با 4.8 ساعت افزایش یافت.

Optimizing the Muffler of a Portable Lawn Mower Engine to reduce Noise Pollution Levels

IntroductionThe most important adverse effects of noise on humans have reduced work efficiency and physiological damaging effects such as increased heart rate, high blood pressure, permanent and temporary hearing loss, impaired vision, disrupting the body apos;s balance system, causing nervous disorders and even nervous disorders. Much of the occupational disturbance is due to acoustic vibrations in agricultural mechanization, which is affecting a large number of farmers. In this regard, most of the noise and vibration come from twostroke or fourstroke engines that are used in lawn mowers, sprayers, pits and more. These highvibration equipment causes a great deal of damage to their operators. Portable lawn mowers are popular for working in urban and rural areas due to their low cost, low maintenance cost, high maneuverability and affordability. Therefore, the possibility of optimizing the muffler of a small combustion engine for a lawn mower was investigated and studied in the present stud.Materials and MethodsTo optimize the existing muffler, geometry of the factory muffler was first redesigned in solidworks 2014 software. Then the optimized muffler, along with the factory muffler exported into ANSYS CFX software and simulated in terms of velocity and pressure distributions. To evaluate the built muffler and compare its performance with the factory standard muffler, the mufflers were then mounted on a DOMA’s lawnmower model WPGD501 with a 42 cm3 engine volume and tested outdoors in a radius of 5 m. All sound recording tests were performed in steady state at a distance of 1m with a 45° angle and position along the exhaust outlet to reconstruct the user apos;s ear position. A digital thermometer TEM8820 and a PSAV01 digital barometer were used to measure the sound pressure and an environment temperature.Results and DiscussionThe results showed that at 3000 rpm, the sound pressure level of the modified muffler decreased by 6.4% compared to the modified muffler. The same decrease in sound pressure level was achieved at 5000 rpm, equal to 4.5%. The results of this study showed that with increasing engine speed, pressure changes in the muffler had an upward trend. These changes in the modified muffler increased by 0.02 kPa at 3000 rpm and by 0.07 kPa at 5000 rpm. According to the outputs of the FFT diagrams, the intensity and amplitude of the output frequencies from the modified muffler significantly decreased almost at most frequencies. Therefore, effective pressure difference (ΔPrms) was used for the further investigations. The results of this study showed that the pressure changes in the muffler had an upward trend with increasing the engine speed. These changes in the modified muffler increased by 0.02 kPa at 3000 rpm and by 0.07 kPa at 5000 rpm.ConclusionsAccording to the results of the present study, by optimizing the internal muffler geometry of the lawnmowers by installing internal blades and neutralizing the sound intensity inside the muffler, it is possible to reduce the sound pressure level by 4% to about 7% over the original muffler. It is a very simple and inexpensive method for the manufacturers of such engines.