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    A thermodynamic approach to compare the performance of rhombic-drive and crank-drive mechanisms for a beta-type Stirling engine
    (Elsevier Ltd, 2016) Aksoy, Fatih; Solmaz, Hamit; Karabulut, Halit; Çınar, Can; Özgören, Yaşar Önder; Polat, Seyfi
    In this study, the effect of rhombic drive and crank drive mechanisms on the performance of a beta-type Stirling engine was investigated by nodal analysis. Kinematic and thermodynamic relations for both drive mechanisms were introduced and a Fortran code was written for the solution. Piston strokes, cylinder and displacer diameters, hot and cold end temperatures, regenerator volumes and heat transfer surface areas were taken equal for both engines with two different drive mechanisms. In the analysis, air was used as the working gas. Engine power and efficiency were compared for different charge pressure values, working gas mass values, heat transfer coefficients and hot end temperatures. Maximum specific engine power was 1410 W/L for the engine with rhombic drive mechanism and 1200 W/L for the engine with crank drive mechanism at 4 bars of charge pressure and 500 W/m2K heat transfer coefficient. Rhombic drive mechanism was relatively advantageous at low working gas mass values and high hot end temperatures. In comparison with the engine having rhombic drive mechanism, the relatively poor kinematic behaviour of the engine having crank drive mechanism caused lower engine efficiency and performance. Heat transfer coefficient was also predicted by using an experimental pressure trace. © 2015 Elsevier Ltd.
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    The Effects of iso-propanol and n-heptane Fuel Blends on HCCI combustion characteristics and engine performance
    (2015) İpci, Duygu; Yılmaz, Emre; Aksoy, Fatih; Uyumaz, Ahmet; Polat, Seyfi; Solmaz, Hamit
    In this study, the effects of iso-propanol fuel blends were investigated on HCCI combustion and engine performance. The variations of cylinder pressure, heat release rate, start of combustion and engine performance were studied in a single cylinder, four stroke, gasoline HCCI engine. The experiments were conducted at different inlet air temperatures at constant air excessive coefficient (λ=2) and engine speed (1500 rpm). The test results showed that cylinder pressure and heat release rate delayed with the addition of iso-propanol in the test fuels. It was also found that the increase of inlet air temperature causes to advance the combustion. Iso-propanol has higher octane number compared to conventional fuels. However, calorific value of iso-propanol is lower than conventional fuels. The aim of this study is to research the usage of iso-propanol in HCCI engines. The experimental findings showed that the tendency of knocking combustion decreased with the increase of the amount of iso-propanol. The start of combustion was delayed with the increase of the amount of iso-propanol. In addition, combustion duration decreased with the addition of iso-propanol in HCCI combustion. As a result, knocking can be prevented using iso-propanol in HCCI engines. This effect also led to extend the HCCI operating range
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    Thermodynamic comparison of crank-drive and rhombic-drive mechanisms for a single cylinder spark ignition engine
    (Gazi Univ, Fac Engineering Architecture, 2020) Yilmaz, Emre; Polat, Seyfi; Solmaz, Hamit; Aksoy, Fatih; Cinar, Can
    In internal combustion engines, power is taken from a shaft and motor movement is defined by the angular motion of this shaft. This movement refers to the angle of the gear in rhombic drive mechanism engines while taking the name of the crank angle in crankshaft engines. In this study, thermodynamic comparison was performed in a single cylinder, four-stroke spark ignition engine with crank-drive and alternative rhombic drive mechanisms. Maximum cylinder pressure was obtained at 371 degrees for both rhombic drive and crank mechanism. The maximum cylinder pressure of the crank mechanism is 63.1 bar while the maximum cylinder pressure of the rhombic drive mechanism is 64.5 bar. While in the rhombic drive mechanism engine, the amount of heat lost from the cylinder wall is 15.27 J in one cycle, this value is calculated as 13.68 J with a crank mechanism for a cycle.