Investigation on Multiple Injection Strategies for Gasoline PPC Operation in a Newly Designed 2-Stroke HSDI Compression Ignition Engine

Partially Premixed Combustion (PPC) of fuels in the gasoline octane range has proven its potential to achieve simultaneous reduction in soot and NOX emissions, combined with high indicated efficiencies; while still retaining proper control over combustion phasing with the injection event, contrary to fully premixed strategies. However, gasoline fuels with high octane number as the commonly available for the public provide a challenge to ensure reliable ignition especially in the low load range, while fuel blends with lower octane numbers present problems for extending the ignition delay in the high load range and avoid the onset of knocking-like combustion. Thus, choosing an appropriate fuel and injection strategy is critical to solve these issues, assuring successful PPC operation in the full engine map. In this framework, the objective of the present investigation consists of evaluating the use of multiple injection strategies for achieving stable PPC operation, attaining low NOX and soot emissions together with high efficiencies. This research was carried out in a single-cylinder DOHC 2-stroke HSDI CI engine using 95 Research Octane Number (RON) gasoline fuel. Three different operating conditions in terms of indicated mean effective pressure (IMEP) and speed were investigated: 3.1 bar IMEP and 1250 rpm, 5.5 bar IMEP and 1500 rpm and 10.4 bar IMEP and 1500 rpm. Parametric variations of injection timings, at different rail pressures and different fuel split between injections were experimentally performed to analyze the effect of the injection strategy over the combustion process, exhaust emissions and efficiency levels. Experimental results confirm how using an appropriate injection strategy helps to achieve stable PPC operation in the selected operating conditions; with competitive combustion stability, lower NOX and soot levels, and moderate CO and HC emissions with combustion efficiency over 96%, compared to Conventional Diesel Combustion (CDC). Finally, a detailed analysis of the local cylinder conditions was performed by means of 3D-CFD simulations in order to provide guidelines for further optimization of the gasoline PPC concept, when using multiple injection strategies in the 2-stroke engine under development.Benajes Calvo, JV.; Novella Rosa, R.; De Lima Moradell, DA.; Tribotte, P. (2015). Investigation on Multiple Injection Strategies for Gasoline PPC Operation in a Newly Designed 2-Stroke HSDI Compression Ignition Engine. SAE International Journal of Engines. 8(2):758-774. doi:10.4271/2015-01-0830S7587748

High load performance and combustion analysis of a four-valve direct injection gasoline engine running in the two-stroke cycle

With the introduction of CO2 emissions legislation or fuel economy standards in Europe and many countries, significant effort is being made to improve spark ignition gasoline engines because of their dominant market share in passenger cars and potential for better fuel economy. Amongst several approaches, the engine downsizing technology has been adopted by the automotive companies as one of the most effective methods to reduce fuel consumption of gasoline engines. However, aggressive engine downsizing is constrained by excessive thermal and mechanical loads as well as knocking combustion and low speed pre-ignition (also known as super-knock). In order to overcome such difficulties, a gasoline direct injection single cylinder engine was modified to run under the two-stroke cycle by operating the intake and exhaust valves around bottom dead centre (BDC) at every crankshaft revolution. The combustion products were scavenged by means of a reversed tumble flow of compressed air during the positive valve overlap period at BDC. The engine output was determined by the charging and trapping efficiencies, which were directly influenced by the intake and exhaust valve timings and boost pressures. In this research a valve timing optimisation study was performed using a fully flexible valve train unit, where the intake and exhaust valve timings were advanced and retarded independently at several speeds and loads. A supercharger was used to vary the load by increasing the intake pressure. The effects of valve timing and boost pressure in this two-stroke poppet valve engine were investigated by a detailed analysis of the gas exchange process and combustion heat release. Gaseous and smoke emissions were measured and analysed. The results confirmed that the two-stroke cycle operation enabled the indicated mean effective pressure to reach 1.2MPa (equivalent to 2.4MPa in a four-stroke cycle) with an in-cylinder pressure below 7MPa at an engine speed as low as 800rpm. The engine operation was limited by scavenging inefficiencies and short time available for proper air-fuel mixing at high speeds using the current fuel injector. The large amounts of hot residual gas trapped induced controlled auto-ignition combustion at high speeds, and thus the abrupt heat release limited higher loads.The Brazilian council for scientific and technological development (CNPq – Brasil

An adapted heat transfer model for engines with tumble motion

In the last years, a growing interest about increasing the engine efficiency has led to the development of new engine technologies. The accurate determination of the heat transfer across the combustion chamber walls is highly relevant to perform a valid thermal balance while evaluating the potential of new engine concepts. Several works dealing with heat transfer correlations that consider the swirl motion are found in the literature; however, there is a lack of works dealing with heat transfer correlations which take into account the effect of the tumble movement. In this work, a new heat transfer model accounting for the tumble motion is presented. A two stroke HSDI Diesel engine with high tumble and no swirl is used to perform the theoretical study, the model development and its final calibration. Initially, a theoretical analysis of the gas movement phenomena is carried out based on CFD results and then, a model is developed and calibrated based on a skip-fire testing technique. Finally, a sensitivity study focused on evaluating the model robustness is performed. The results confirm an average RMSE reduction of 70% with respect to the Woschni model, being this consistent improvement qualitatively evidenced in the instantaneous heat transfer evolutionThe support of the Spanish Ministry of Economy and Competitiveness (TRA2013-41348-R) is greatly acknowledged.Olmeda González, PC.; Martín Díaz, J.; Novella Rosa, R.; Carreño, R. (2015). An adapted heat transfer model for engines with tumble motion. Applied Energy. 158:190-202. https://doi.org/10.1016/j.apenergy.2015.08.051S19020215

Analysis of the combustion process, pollutant emissions and efficiency of an innovative 2-stroke HSDI engine designed for automotive applications

[EN] On the last years engine researchers has been focused on improving engine efficiency in order to decrease CO2 emissions and fuel consumption, while fulfilling the increasingly stringent pollutant emissions regulations. In this framework, engine downsizing arises as a promising solution, and 2-stroke cycle operation offers the possibility of reducing the number of cylinders without incurring in NVH penalties. An experimental investigation has been performed to evaluate the performance of a newly-designed poppet valves 2-stroke engine, in terms of finding the proper in-cylinder conditions to fulfill the emission limits in terms of NOx and soot, keeping competitive fuel consumption levels. Moreover, present research work aims to improve the existing knowledge about the gas exchange processes in a 2-stroke engine with poppet valves architecture, and its impact over the combustion conditions, final exhaust emissions levels and engine efficiency. The experimental results confirm how this engine architecture presents high flexibility in terms of air management control to substantially affect the in-cylinder conditions. The in-cylinder oxygen concentration and density, which are the product of a given trapping ratio and delivered mass flow, were linked to pollutant emissions and performance by their impact on instantaneous adiabatic flame temperature and spray mixing conditions. After the optimization process, it was possible to minimize simultaneously NOx, soot and indicated fuel consumption, without observing a critical trade-off between the pollutant emissions and the fuel consumption. (C) 2013 Elsevier Ltd. All rights reserved.This research has been sponsored by the European Union in framework of the POWERFUL project, seventh framework program FP7/2007-2013, theme 7, sustainable surface transport, grant agreement No. SCP8-GA-2009-234032. The authors gratefully appreciate this support.Benajes Calvo, JV.; Novella Rosa, R.; De Lima Moradell, DA.; Tribotte, P.; Quechon, N.; Obernesser, P.; Dugue, V. (2013). Analysis of the combustion process, pollutant emissions and efficiency of an innovative 2-stroke HSDI engine designed for automotive applications. Applied Thermal Engineering. 58(1-2):181-193. https://doi.org/10.1016/j.applthermaleng.2013.03.050S181193581-

Comparaison de méthodes de suivi de l'occupation du sol pendant 50 ans à partir de photos aériennes et satellites dans un bassin sahélien

International audienceLand use/cover change (LUCC) is a major indicator of the impacts of climate change and human activity, particularly in the Sahel, where the land cover has changed greatly over the last 50 years. Aerial and satellite sensors have been taking images of the earth's surface for several decades, providing repeated, systematic coverage of large areas that offers a unique documentary source for characterizing change in environmental resources. These data have been widely used to monitor LUCC, but many questions remain concerning what type of pre-processing should be carried out on image resolutions and which methods are most appropriate for successfully mapping patterns and dynamics in both croplands and natural vegetation. This paper aims at considering those methodological questions. It uses multi-source imagery from 1952 to 2003 (aerial photographs, Corona, Landsat MSS, Landsat TM and SPOT 5) and pursues two objectives: i) to implement and compare a number of processing chains on the basis of multi-sensor data, in order ii) to accurately track and quantify LUCC in a 100 km² Sahelian area over 50 years. The heterogeneity of the images' spatial and spectral resolutions led us to compare post-classification comparison methods aimed at producing coherent diachronic maps based on a common land-cover nomenclature. Three main approaches were tested: pixel-based classification, vector-grid-based on-screen interpretation and object-oriented classification. Within the automated approaches, we also examined the influence of spectral synthesis and spatial homogenization of the data through the use of composite bands (principal components analysis, indices) and by resampling images at a common resolution. Classification accuracy was estimated by computing confusion matrices, by analyzing overall change in the relative areas of land use/cover types and by studying the geographical coherence of the changes. These analyses indicated that on-screen interpretation was the most suitable approach for providing coherent, valid results from the multi-source images available over the study period. However, satisfactory classifications were obtained with the pixel-based and object-oriented approaches. The results also showed significant sensitivity, depending on the method considered, to the combinations of bands used and to resampling. Lastly, the 50-year trends in LUCC indicated a large increase in croplands and erosional surfaces with sparse vegetation and a drastic reduction in woody covers

Two strokes Diesel engine - Promising solution to reduce CO2 emissions

Two-stroke engines have dropped out of the automobile market for a long time due to severe drawbacks. Unfortunately, the comparison with the performances of four-stroke engines was not in favour of two-stroke ones. Nevertheless, the needs of a more compact engine with a better ratio of the mass and size versus power motivated research efforts at the beginning of the 90's. Regrettably, these efforts did not result in commercial success and automobile manufacturers kept four-stroke engine architecture as base architecture. However, the two-stroke engine is a highly favourable concept for downsizing and cost reduction by reducing the number of cylinders without NVH penalties. All that added to the maturity of CFD calculations and the availability of high power electronic for control and fuel injection encouraged the Renault research division to have a closer look into its architecture. The study deals with a two-cylinder Diesel engine based on two-stroke valves engine. Air admission and exhausts gas are done through four valves per cylinder; fuel injection is done through ten holes nozzle at 1800 bar of pressure. The company Delphi, partner of the project, provided the injection system. The displacement of engine is 730 cm3 and the engine is designed for a range of power of about 35-50 kW and a range of torque of 110 - 145 N.m. The design of the scavenging was achieved with the help of 3D simulation based on the best 3D simulation tools available. More than 250 calculations were completed to determine the best design of the cylinder-head reaching the objective of scavenging performances. At the end of this step, the best compromise was determined between the mass of fresh gas and the mass of burnt gas in the cylinder respecting combustion and engine efficiency criterias. Air supercharging system was designed in cooperation between the partners Renault, Le Moteur Moderne and University of Technology of Prague. The injection and combustion testing and optimisation were done on a one cylinder engine at CMT, University of Valencia, partner of the project. The set of parameters was explored and optimised to reach the best compromise between the combustion efficiency and the target of pollutant emissions to reach the EURO 6 standards. Finally, the optimisation of the engine, including the air loop system, calibration and control is planed in 2012 and will be done at IFPEN, partner of project. The objectives, the design process, the major technical breakthrough as well as its detailed results will be presented in this paper.The work was split between the partners of the project supported by the European Commission.Tribotte, P.; Ravet, F.; Dugue, V.; Obernesser, P.; Quenchon, N.; Benajes Calvo, JV.; Novella Rosa, R.... (2012). Two strokes Diesel engine - Promising solution to reduce CO2 emissions. Procedia - Social and Behavioral Sciences. 48:2295-2314. doi:10.1016/j.sbspro.2012.06.1202S229523144

Friction and wear of a piston ring/cylinder liner at the top dead centre: experimental study and modelling

Wear assessment of critical components subjected to relative sliding is a key factor for the development of advanced materials and surface treatments in automotive industry. Simulation of wear process of the engine components is considered as a good alternative for experimental testing which is costly and time-consuming, but it requires a reliable experimental data for model fine-tuning. Therefore, friction and wear of cylinder liner against a piston ring were experimentally studied in simulated laboratory tests. The parameters which were controlled in these tests included oil type, lubrication starvation, surface finishing and surface coatings. The obtained experimental data were fed into a specific simulation model (AVL Excite-Power Unit). Comparison of experimental and simulated results yielded the error below 5%.The authors acknowledge the European Commission for funding of the European Project “Powerful” under Contract 234032