AIMS Energy, 2018, 6(6): 1050-1066. doi: 10.3934/energy.2018.6.1050

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Validated analytical modelling of frequency-based aspects, eccentricity and stress concentration in diesel engines with flexible crankshaft

ISEC Program, Faculty of Engineering, Xiamen University of Technology (XMUT), Jimei District, Xiamen, Fujian Province, P.R. China

Diesel engines provide higher power but exhibit much larger in-cylinder pressure and dynamic loading on crankshaft than those of spark ignition engines. Optimizing the fuel consumption in diesel engines holds the potential to improve transport sustainability. The flexibility of the crankshaft of diesel engines exhibits significant nonlinearities in the analysis of diesel powertrains performance. Particularly, at crankshaft rotational speeds of higher than 2000 rpm the influence of the flexibility of the crankshaft of diesel engine on diesel powertrains performance becomes obvious. Analytical modelling of such dynamics of diesel engines is yet to be done. Thus, the frequency-based aspect of the analysis of flexible crankshaft has been investigated. The stiffness and natural frequency of crankshaft have been thus analytically modeled. Also, the effect of eccentricity in flexible crankshaft on crankshaft and piston secondary motion has been analyzed. The study hence analytically modeled the eccentricity of the crankshaft as the summation of the hydrodynamic eccentricity of the crankshaft and the dynamic mass eccentricity of the crankshaft. The absolute value of the dynamic displacement of the center of the crankshaft due to vibration has been therefore analytically modeled. The analytical modelling of the dynamic displacement in flexible crankshaft has been validated using a case study showing a relative error of 2.7%. Moreover, the study has proposed remedying the stress concentration in the most critical section in crankshaft by identifying: (i) the location of the most critical section of stress concentration in crankshaft, (ii) the effect of the radius of the crankpin shoulder fillet on the maximum shearing stress that can carried by the crankpin. Thus, the present paper has identified the value of the radius of the crankpin shoulder fillet that remedies the stress concentration in the most critical section of stress concentration in crankshaft. This developed model holds the potential to optimize fuel consumption and improve transport sustainability.
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