Performance evaluation of an ethanol-fueled engine with EGR to reduce NOx emissions and to control knock

Abstract

In Brazil there has been investments in research aimed at the agricultural sector in the planting of sugar cane, as well as in the industrial phase of ethanol production. But, after the 80's, when automakers stopped making cars with engines dedicated to ethanol, there was a stagnation in the study of improvements to the ethanol engines. Despite the onset of the flex-fuel engine able to operate also with ethanol, there are more studies for spark ignition engines using gasoline or mixtures than with straight ethanol. The objective of this project is to contribute to the technological advancement of spark-ignition ethanol engines, assessing the possibilities of a heavily loaded engine adopting exhaust gas recirculation (EGR) to reduce NOx and control the detonation. Connection of this Thesis with the Research Project FAPESP 2013/50238-3The work proposed for this PhD is associated with the Sub-theme 4 named "Thermodynamic simulation of indicated performance for ethanol engines" (item 7.4.4 of the Project, p.23 and 24). Graduate students (Master and PhD) will form a team with the post-doc researcher and the coordinator of sub-theme 4. The work of this student relates specifically to the activities 7.4.4e) (year 2 Scheduled activities - p.29) and 7.4.4f) (year 3 Scheduled activities - p.30).Main objectives of this work: - Identify the detonation limits for the heavily loaded ethanol engine with high compression ratio. - Identify the role of exhaust gas recirculation (EGR) to the control of the detonation and to reduce NOx emissions; Brief activities description: - Literature review- Calculation of thermodynamic properties of gas mixtures (air, fuel and combustion products) - including NOx formation model. - Development of a semi-empirical model to predict the detonation borderline in ethanol engines; - Validation of detonation model through experimental results; - Incorporation of the EGR effects on the thermodynamic simulation model for ethanol engines.- Evaluation of expected emissions of NOx due to the amount of EGR adopted. Methodology: For the development of engine model will be applied the concepts of mass and energy conservation (first law of thermodynamics) and entropy generation (Second Law of Thermodynamics), both for the open phase and to the closed phase of the cycle. The thermodynamic properties of each substance present in the gases will be obtained as a function of the instantaneous temperature using JANAF (1971) thermochemical data. For the calculation of the molar fractions of the substances in the exhaust gases will be considered the chemical equilibrium as a function of instantaneous pressure and temperature. In the case of nitrogen oxides, a simplified model of chemical kinetics will be assumed. It will be assumed a phenomenological model to estimate the heat transfer between the gases and the engine walls. Likewise, the combustion process will be evaluated on the assumption two zones with instantaneous equilibrium of pressure, but with different temperatures in the regions of the burned and unburned gases. The burning rate will be modeled by a Wiebe function, with parameters adjusted to each engine operating condition. It will be developed a phenomenological model to predict the ignition delay of the mixture, which will also be used to predict detonation borderline. The exhaust gas recirculation (EGR) will be incorporated in some operating regimes of the engine, causing changes in the composition of the fresh mixture and affecting the energy available for combustion. The validation of the simulation model will be performed by comparison with experimental results obtained in engine test bench of Maua Institute of Technology. The geometric data will be those of the engine which is the basis for the FAPESP / PCBA Project. (AU)