Simulation on atkinson-miller cycle engine of four stroke two-wheel vehicle for light operating condition
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Date
2017-10-01
Authors
Sobana Raj Subramonian
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Abstract
Standard engine found in motorcycles are based on Otto cycle. The Otto cycle engine utilize the maximum amount of power is found to be efficient only at heavy operating condition such as maximum total mass, low tire pressure and maximum drag due to maximum frontal area. Consequently, this maximum power has been wasted for the light operating condition usage. Due to short expansion stroke in the Otto cycle, the system was unable to fully utilize the heat generated. Hence, extra heat has been ejected to the environment through the exhaust and engine block cooling system. However, the Atkinson-Miller cycle engine application with higher compression ratio is able to solve the problem. The objective is to investigate the behavior of the Atkinson-Miller cycle spark ignition engine with high compression ratio of a motorcycle engine. This research involves one dimensional analysis using Ricardo WAVE to find the engine output data and the advantage and disadvantages of having high compression ratio of the Atkinson-Miller cycle spark ignition engine can be predicted. Further to this, three dimensional analysis is performed using ANSYS Fluent to conduct the investigation mainly on fuel knocking due to high compression pressure. The three dimensional simulations predict on the gas density, gas pressure and gas temperature profile. It has been found that, an increase in the heat flux through engine block coupled with high temperature exhaust gas exiting the exhaust port consequently decreases both total net work output and the thermal efficiency. The amount of heat ejected through the exhaust is lower in the Atkinson-Miller cycle engine compared to the Otto cycle engine mainly due to the greater expansion. However, with the application of the Miller cycle concept in the over expanded cycle, the engine experiences losses in brake power, brake engine torque and brake thermal efficiency. The low torque and lower brake power is found to be downside of this Atkinson-Miller cycle engine but, the brake power and torque drastically improved after engine compression ratio increased to 20:1. However, three dimensional analysis of the Atkinson-Miller cycle found the engine to experience fuel knocking for compression ratio above 11:1. Consequently, the stand alone operation of Atkinson-Miller cycle is insufficient. Therefore, the Atkinson-Miller cycle engine are coupled with high compression ratio, 11:1. The high compression ratio Atkinson-Miller cycle engine has improved fuel consumption for light load/operating condition (minimum total mass, optimum tire pressure and minimum drag due to minimum frontal area). The Atkinson-Miller cycle engine (10 degree LEVO and 15 degree LIVC) at compression ratio of 11:1 (A10M15_RC11) reduces fuel consumption by 1 percent at light load and 5 percent at heavy load condition for suburban and urban drive pattern. For highway drive pattern, fuel consumption reduced by 2.9 to 3 percent for both load condition. However, A10M15_RC11 cycle engine experiences high heat transfer rate during compression stroke and combustion compared to the Otto cycle engine but has low heat transfer rate during power and exhaust stroke which reduces intake gas temperature. This situation concludes that, A10M15_RC11 cycle engine has low fuel consumption and high brake thermal efficiency for both load conditions.