A simple approach for comparing performance of gasoline general-purpose engines at maximum power

Abstract

The single or double cylinder, low power output engines used in machines such as garden hoe machines, chainsaws, generators, lawnmowers, mini tractors are called general-purpose engines. Each engine manufacturer has engines with its own unique structural designs. The power of these engines generally varies depending on the swept volume. However, when the engine catalogs are examined, the characteristics such as stroke ratio, maximum power speed, and compression ratio are different. In this study, we present a simple thermodynamic model in which the gasoline general-purpose engines, whose swept volume, compression ratio and stroke ratio are different, can be compared by taking into account their performance at maximum power, friction, irreversibility, exhaust and heat losses. For the numerical study, by comparing the physical properties of 10 general purpose engines of 5 different manufacturers, their performance was compared by performing thermodynamic modeling in the conditions where they produced maximum power. The power values in the catalogs of the engines and the power values calculated according to the thermodynamic model were very close to each other and this thermodynamic model was used. According to the thermodynamic model, maximum cycle temperatures, specific fuel consumption and power density of the motors were compared. In addition, the heat balance of each engines is created. Regardless of the brand, model and stroke volume and effective power, engine parameters are examined according to stroke ratio and specific fuel consumption. As a result of the study, the maximum cycle temperature, power density and mechanical efficiency decrease with the increase in the specific fuel consumption and the stroke ratio. However, the increase in the stroke ratio increases the specific fuel consumption. According to the obtained results, it is seen that the characteristics such as course rate and compression ratio as well as simple properties such as stroke volume and engine power are important and effective parameters for comparison. As a result of this study, it can be seen that the thermodynamic model presented can be used to compare gasoline general purpose engines with different physical properties.

Keywords

• General purpose engine
• engine performance
• Otto cycle
• gasoline engines

Benzinli genel amaçlı motorların maksimum güçteki performanslarının karşılaştırılması için basit bir yaklaşım

Öz

Bahçe çapa makineleri, zincirli testereleri, jeneratörler, çim biçme makineleri, mini traktörler gibi makinelerde kullanılan tek veya çift silindirli, düşük güç çıkışlı motorlar genel amaçlı motorlar olarak adlandırılmaktadır. Her motor üreticisinin kendine özgü yapısal tasarımlara sahip motorları bulunmaktadır. Bu motorların güçleri genel olarak kurs hacmine bağlı olarak değişmektedir. Ancak motor katalogları incelendiğinde kurs oranı, maksimum güçteki hızı ve sıkıştırma oranı gibi karakteristik özellikleri birbirinden farklıdır. Bu çalışmada kurs hacmi, sıkıştırma oranı ve kurs oranı birbirinden farklı olan benzinli genel amaçlı motorların maksimum güçteki performansları, sürtünme, tersinmezlik, egzoz ve ısı kayıpları da dikkate alınarak karşılaştırılabildiği basit bir termodinamik model sunulmuştur. Sayısal çalışma için 5 farklı üreticiye ait 10 adet genel amaçlı motorun fiziksel özellikleri referans alınarak maksimum güç ürettikleri şartlarda termodinamik modellemeleri yapılarak performansları karşılaştırılmıştır. Motorlara ait kataloglardaki güç değerleri ile termodinamik modele göre hesaplanan güç değerleri birbirine oldukça yakın çıkmıştır ve bu termodinamik modelin kullanılabilir olduğunu göstermektedir. Oluşturulan termodinamik modele göre motorların maksimum çevrim sıcaklıkları, özgül yakıt tüketimleri ve güç yoğulukları karşılaştırılmıştır. Ayrıca her motora ait ısı balansı oluşturulmuştur. Marka, model ve kurs hacmi ve efektif gücünden bağımsız olarak motor parametreleri kurs oranı ve özgül yakıt tüketimine bağlı olarak incelenmiştir. Yapılan inceleme neticesinde özgül yakıt tüketimi ve kurs oranının artmasıyla birlikte maksimum çevrim sıcaklığı, güç yoğunluğu ve mekanik verimde azalma meydana gelmektedir. Bununla birlikte kurs oranının artması özgül yakıt tüketimini de artırmaktadır. Elde edilen sonuçlara göre motorların karşılaştırılması için yalnızca kurs hacmi ve motor gücü gibi basit özelliklerin yanında kurs oranı, sıkıştırma oranı gibi özelliklerin de karşılaştırma için önemli ve etkili parametreler olduğu görülmüştür. Bu çalışma neticesinde, sunulan termodinamik modelin farklı fiziksel özelliklere sahip benzinli genel amaçlı motorların karşılaştırılabilmesi için kullanılabileceği görülmüştür. 

Anahtar Kelimeler

• Genel amaçlı motor
• motor performansı
• Otto çevrimi

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