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As emissions regulations become more and more stringent and conventional fuel sources rarefaction, new alternatives are emerging to address this situation. Dual fuel engines are among the promising solutions, offering both ecological and economic advantages. However, these engines often confront constraints linked to high levels of unburnt hydrocarbons (HC) at low loads and NOx emissions at high loads. To overcome these problems and guarantee high-efficiency overall operating loads, exhaust gas recirculation (EGR) is a potential solution. In the present experimental study, appropriate modifications have been carried out to a single-cylinder diesel engine to ensure dual fuel operation with EGR. Natural gas and diesel are used as the primary and pilot fuel, respectively. At low load operations, the EGR rate is increased up to 35% until the reduction of unburnt hydrocarbons. However, at high loads, the EGR rate is carefully adjusted, as the combustion efficiency easily deteriorates due to oxygen amount lack in the combustion chamber. Also, minimizing NOx emissions is prioritized in all load conditions while keeping thermal efficiency in sight. In addition, the variation in the amount of pilot fuel is studied for improving the combination of dual fuel engine operation with the EGR technique. This made it possible to determine the influence of load, EGR rate, and pilot fuel quantity on the engine in response to the triple challenges of reducing NOx and HC and improving thermal efficiency. The results show that an adequate EGR rate of 30%, depending on the operating conditions, can reduce HC emissions by >25% while increasing thermal efficiency by around 20%. This result is accompanied by a significant reduction, over 90%, in NOx emissions. [ABSTRACT FROM AUTHOR]

The aim of the present paper is to investigate numerically the heat transfer within exhaust valves by considering the actual boundary conditions provided from an internal combustion engine at differentload and speed. For this purpose, the valve is subdivided into seven adequate subdivisions to better assess the effect of each engine parts, therefore, an average value of the transient heat transfer coefficient (HTC) and the adiabatic wall temperature (AWT) for each subdivisions are evaluated during one cycle. These two parameters are introduced as boundary condition in a FEM model. The simulations are done at diverse engine regime, and therefore, the trend of the real boundary condition in term of HTC and AWT are given versus engine speed at different load. The findings show that the HTC increases linearly with engine speed however, the AWT decrease slightly at partial load and increase in the case of full engine load. The obtained model is used to highlight the temperature map, which will certainly help to avoid any damage to the exhaust valve.

The present paper proposes a novel methodology of turbocharging automotive engines to reach targeted performance. The actual method is tested and validated against simulation test results of two turbocharged diesel engines; engine I, three cylinders, 1.5 L, and engine II, six cylinders, 5.9 L. The present procedure is subdivided into four key parts; namely, database construction, selection procedure, turbocharger preliminary design, and engine modeling. Based on geometric dimensions and aerodynamic parameters provided by the preliminary design procedure, 3D geometries of the turbine and compressor are generated for each studied engine. After integrating previous data into a constructed turbocharger database, two turbochargers are selected for the engine I, while only one turbocharger for the engine II. The findings show that, at the engine speed of 4000 rpm, engine I matched with the adequate turbocharger reached a target power about 2.7%, compared to the original turbocharger equipping engine I. Furthermore, engine II reached a rated power of 299.3 kW at 2500 rpm which is slightly under the original one by 2.64 kW. The superimposition of the engine operating area on compressor and turbine maps provided satisfactory results in terms of turbocharger-engine output performance, fuel consumption, secure functioning and engine thermal strength. Finally, the main advantage of the developed methodology consists of its ability to be applied at both earlier and last stages of the engine turbocharging process or to find new adequate turbochargers to replace the original one for economic, mechanical or for safety reasons. [ABSTRACT FROM AUTHOR]

The waste derived syngas allows the recovering of its energy using conventional technologies of energy production like internal combustion engines. However, its major drawback is its low calorific value and low stoichiometric air fuel ratio leading to higher specific fuel consumption and difficulties when using injection mode due to the required long injection duration. Recently, many studies aimed to improve the calorific value of the syngas, either by enriching it with methane or by optimizing the production techniques and the used feedstock like the refused derived fuel (RDF). Syngas produced by the pyrolysis of RDF is a methane rich syngas (40-60%) with a relatively high calorific value and stoichiometric air fuel ratio. This work is an experimental study on the combustion, performance and emissions of this type of syngas in spark ignition engine taking into consideration its composition variability. Pure methane was also tested and is considered as a reference fuel for comparison. The results show a faster and smoother combustion of syngas, lower emissions of total hydrocarbons, and higher emissions of nitrogen oxides and carbon monoxide. Beside, syngas improved the brake thermal efficiency while still maintaining higher brake specific fuel consumption with respect to methane. [ABSTRACT FROM AUTHOR]

The valves of an internal combustion engine play an essential role in the automobiles and their surroundings significantly affect their thermo-mechanical behavior. The work aims to assess numerically the effect of the real thermo-mechanical boundary conditions on the valves by considering the actual complex surrounding. For this purpose, we have subdivided the valve into seven adequate zones. We have evaluated the average values of the transient heat transfer coefficient, the adiabatic wall temperature and the mechanical load at each subdivision are during the opening and the closing periods. A transient Finite Element Model under ANSYS APDL software is developed and simulations are carried out until reaching the steady state. The temperature distribution and the thermal stresses at each valve position is obtained and then analyzed. The main findings show that the stress intensity distribution is developed in the zones labelled stem guide port and seat local of large temperature gradients, which causes high thermal stresses responsible of cracks or thermal fatigue damage. In addition, knowing the temperature map, the thermal gradient and stress under actual conditions will surely help manufacturers to better design exhaust valve, avoid early failure and enhance the durability of valves. [ABSTRACT FROM AUTHOR]

This study is concerned with the analyses of heat transfer through an exhaust valve considering the real unsteady effects during the cycle of an internal combustion engine and to identify the factors and parameters affecting the heat transfer. The valve is segmented into several zones to facilitate incorporating the boundary conditions and evaluating the heat transfer coefficient and the adiabatic wall temperature based on the finite element method. The unsteady simulations were carried out using ANSYS-APDL for the proposed thermal model. The effect of lubricating oil and the contact resistance between guide and engine block and the thermal contact between exhaust valve and seat are included, as well as the differential displacement of both the guide and engine block walls due to high working temperature. The averaged values of heat transfer coefficient and adiabatic wall temperature used in the boundary conditions are shown to underestimate the temperature maps. The cyclic boundary conditions required more run time to reach the steady state and allowed better monitoring of the thermal process. The thermal contact resistance has the main contribution in the zone of valve-seat, whereas the resistance of oil film between the guide and stem valve is shown to affect mainly heat transfer coefficient. The obtained maps of temperature reveal the locations of maximum temperatures in the exhaust valve. [ABSTRACT FROM AUTHOR]