Evaluation of the Thermal NO formation mechanism under low-temperature diesel combustion conditions

Over the past two decades, the amount of exhaust gas pollutants emissions has been significantly reduced due to the severe emission legislation imposed in most countries worldwide. Initial strategies simply required the employment of simple after-treatment and engine control devices; however, as the restrictions become more stringent, these strategies are evolving in the development of different combustion modes, specially characterized by having low-temperature combustion characteristics. These new working conditions demand the need to check the suitability of the current NO predictive models that coexist nowadays under standard diesel combustion characteristics, paying closer attention to the Thermal mechanism. In order to do so, a common chemical-kinetic software was employed to simulate, for n-heptane and methane fuels, fixed local conditions (standard diesel and low-temperature combustion) described by constant pressure, relative mixture fraction, oxygen mass fraction and initial and final reaction temperature. The study reflects a common trend between all the studied cases, independently of the considered local conditions, making it applicable to more complex situations such as real NO formation processes in diesel sprays. This relationship was characterized by a fourth-degree polynomial equation capable of substantially improving the NO prediction by just using the Thermal NO predictive model.The authors thank the Ministerio de Ciencia e Innovacion of the Spanish government for contributing to this work with the grant BES-2009-021897.Desantes Fernández, JM.; López, JJ.; Redón Lurbe, P.; Arregle, JJP. (2012). Evaluation of the Thermal NO formation mechanism under low-temperature diesel combustion conditions. International Journal of Engine Research. 13(6):531-539. https://doi.org/10.1177/1468087411429638S53153913

Effects of EGR rate on performance and emissions of a diesel power generator fueled by B7

This paper analyses the impacts of the application of an exhaust gas recirculation (EGR) system on the performance and emissions of a stationary, direct-injection diesel engine operating with diesel oil containing 7% biodiesel (B7). Experiments were carried out in a 49-kW diesel power generator with the adapted EGR system, and engine performance and emissions were evaluated for different load and EGR settings. The results were compared with the engine operating with its original configuration without the EGR system, and revealed a reduction of peak cylinder pressure and fuel conversion efficiency, mainly at high engine loads. The use of EGR caused opposite effects on carbon dioxide (CO2), carbon monoxide (CO) and total hydrocarbons (THC) emissions, depending on load and EGR rate, showing an increase in most situations. The application of EGR consistently reduced oxides of nitrogen (NOX) emissions, reaching a maximum reduction close to 30%. In general, the use of EGR increased CO2, CO and THC emissions at high loads. The use of 7.5% EGR was found to be at an adequate rate to simultaneously reduce CO, THC and NOX emissions at low and moderate loads, without major penalties on CO2 emissions and engine performance