Impact of swirl on in-cylinder heat transfer in a light-duty diesel engine

[EN] One of the key strategies to reduce CO2 emissions is to improve the efficiency of engines in order to diminish fuel consumption. A way to increase engine efficiency is to reduce the heat losses. Internal heat transfer in engines depends on combustion chamber conditions. Swirl is an important parameter for combustion that also changes in-cylinder variables relevant to heat transfer. In this work, influence of swirl on combustion chamber heat fluxes was investigated employing wall temperature data and a 0-D thermal model. Local wall temperatures were measured at various locations of the cylinder liner and the cylinder head using thermocouples. A sweep of swirl ratios was carried out at different engine operating conditions. It was observed that the effect of swirl effect was highly dependent on location and was more important near the center of the firedeck. Results from the 0-D thermal model were evaluated by comparing measured and predicted wall temperatures. Using a convenient arrangement of thermocouples and the 0-D thermal model, it was possible to calculate heat flux from combustion chamber to cylinder walls. By analyzing heat flux through the firedeck, an increase in heat losses between 4 and 12% was observed for each unit that swirl number was increased. Results from the 0-D thermal model indicate that similar effects occur for other surfaces in the combustion chamber. (C) 2016 Elsevier Ltd. All rights reserved.The authors acknowledge General Motors Global R&D for supporting this research. The equipment used in this work was partially supported by FEDER project funds "Dotacion de infraestructuras cientifico tecnicas para el Centro Integral de Mejora Energetica y Medioambiental de Sistemas de Transporte (CiMeT), (FEDER-ICTS-2012-06)", framed in the operational program of unique scientific and technical infrastructure of the Ministry of Science and Innovation of Spain.Broatch, A.; Olmeda, P.; García Martínez, A.; Salvador-Iborra, J.; Warey, A. (2017). Impact of swirl on in-cylinder heat transfer in a light-duty diesel engine. Energy. 119:1010-1023. doi:10.1016/j.energy.2016.11.040S1010102311

Evaluation of swirl effect on the Global Energy Balance of a HSDI Diesel engine

[EN] In the last years, a growing interest about increasing engine efficiency has led to the development of new engine technologies. Since air motion in the chamber is a key issue in internal combustion engines to improve the air-fuel mixing process and achieve faster burning rates, modern Diesel engines are designed to generate gas vorticity (swirl) that lead to enhanced turbulence in the combustion chamber. However, the use of swirl has a direct effect on fuel consumption due to the changes in the in-cylinder processes, affecting indicated efficiency, and also on the air management. An analysis, based on the engine Global Energy Balance (GEB), is presented to thoroughly assess the behavior of a high speed direct injection Diesel engine under variable swirl levels at different operating points. The tests have been performed keeping constant both the conditions at intake valve closing and combustion phasing, thus minimizing the variability due to in-cylinder conditions and the combustion process. The analysis includes a combination of theoretical (0D models) and experimental tools (heat rejection and wall temperature measurement) used to ensure control of in-cylinder conditions and to provide detailed explanation of the different phenomena affecting engine efficiency when swirl ratio is modified. Based on these tools, impact of swirl on the engine GEB is analyzed in detail paying special attention to engine efficiency and heat transfer in the chamber. Results show that increasing swirl has two main effects regarding the gross indicated efficiency (eta(i)): on one hand chamber heat rejection increases and therefore eta(i) diminishes about -0.5% at low load and 0.4% at high load; on the other hand combustion development is affected and thus a eta(i) improvement higher to 1.5% is achieved at low load and speed. The combination of these effects leads to a gross indicated efficiency increase higher to 1% at an optimum swirl ratio that diminishes when engine speed increases. In addition, pumping losses effect dominates brake efficiency behavior, which always diminishes (from 0.9% to 1.4%) when swirl increases. (C) 2017 Elsevier Ltd. All rights reserved.The support of GM Global R&D and the Spanish Ministry of Economy and Competitiveness (TRA2013-41348-R) is greatly acknowledged.Benajes, J.; Olmeda, P.; Martín, J.; Blanco-Cavero, D.; Warey, A. (2017). Evaluation of swirl effect on the Global Energy Balance of a HSDI Diesel engine. Energy. 122:168-181. https://doi.org/10.1016/j.energy.2017.01.082S16818112

Swirl ratio and post injection strategies to improve late cycle diffusion combustion in a light-duty diesel engine

[EN] Nitrogen oxides (NOx) and soot emissions are the most important pollutants from direct-injection diesel engines. In particular, soot formation and oxidation determine the net engine-out soot emissions. These phenomena are complex and competing processes during diesel combustion. Despite many researches implicate the mechanisms of soot formation with soot emissions, the enhancement of the late cycle soot oxidation is the dominant mechanism for a reduction of engine-out soot emissions. The mixing process and the in-cylinder bulk temperature are two important parameters in the development of soot oxidation process. The current research compares different engine strategies to enhance the late cycle mixing controlled combustion process and therefore enhance soot oxidation while maintaining similar gross indicated efficiency in a light-duty engine. For this purpose, a simplified methodology has been used, which analyzes the effect of mixing process and in-cylinder bulk gas temperature on soot oxidation during the late cycle combustion. For carrying out this research, theoretical and experimental tools were used. In particular, the experimental measurements were made in a single-cylinder direct-injection light-duty diesel engine varying the swirl ratio and the injection pattern as injection pressure, Start of Energizing (SoE), Energizing Time (ET) and number of injections events. To analyze soot emissions, the combustion luminosity was measured by an optoelectronic probe and the optical thickness parameter (KL) was evaluated by the two-color pyrometry method. The apparent combustion time (ACT-1) was used as mixing time tracer. Results show that an increase in swirl ratio implies an improvement on the mixing process and higher values of average bulk temperature during the late-cycle diffusion combustion. Both phenomena produce an enhancement in the soot oxidation process. In the lowest swirl ratio case, a suitable injection strategy based on multiple injections, provides similar results of soot oxidation process (and therefore, the emissions) as high swirl ratio case. (C) 2017 Elsevier Ltd. All rights reserved.Benajes, J.; Martín, J.; García Martínez, A.; Villalta-Lara, D.; Warey, A. (2017). Swirl ratio and post injection strategies to improve late cycle diffusion combustion in a light-duty diesel engine. Applied Thermal Engineering. 123:365-376. doi:10.1016/j.applthermaleng.2017.05.101S36537612

Experimental study of the influence of exhaust gas recirculation on heat transfer in the firedeck of a direct injection diesel engine

[EN] Emissions control is a key topic for internal combustion engine development. One of the most widespread technologies to reduce the formation of nitrogen oxides is the recirculation of exhaust gas to the engine intake. Besides, carbon dioxide emissions from internal combustion engines can be reduced by increasing engine efficiency. A relevant factor for engine efficiency is heat rejection. The interaction between heat transfer and exhaust gas recirculation is not fully understood. In this paper, an experimental study is presented which aims to shed light on the influence of high pressure exhaust gas recirculation on heat transfer. Three operating points were analyzed. Heat flux was calculated at several locations of the firedeck from temperature measurements. The results showed that the influence of exhaust gas recirculation on heat transfer was significant. Reductions of heat flux up to 18% were observed. The largest reduction was found in the area near the center of the firedeck. To contextualize the findings in the framework of emissions reduction, the trade-off between nitrogen oxides and carbon dioxide was assessed for all test points.The authors acknowledge General Motors Global R&D for supporting this research. The equipment used in this work was partially supported by FEDER project funds Dotación de infraestructuras científico técnicas para el Centro Integral de Mejora Energética y Medioambiental de Sistemas de Transporte (CiMeT), (FEDER-ICTS-2012-06) , framed in the operational program of unique scientific and technical infrastructure of the Ministry of Science and Innovation of Spain. Josep Salvador-Iborra was partially supported through contract FPI-S2-2016-1357 of Programa de Apoyo para la Investigación y Desarrollo (PAID-01-16) of Universitat Politècnica de València.Torregrosa, AJ.; Broatch, A.; Olmeda, P.; Salvador-Iborra, J.; Warey, A. (2017). Experimental study of the influence of exhaust gas recirculation on heat transfer in the firedeck of a direct injection diesel engine. Energy Conversion and Management. 153:304-312. https://doi.org/10.1016/j.enconman.2017.10.003S30431215

Implementation of two color method to investigate late cycle soot oxidation process in a CI engine under low load conditions

[EN] Soot emissions from diesel engines are an important concern in meeting emissions regulations. Soot emissions are the result of two competing processes: soot formation and soot oxidation. Mechanisms of soot formation are discussed extensively in the literature. Equivalence ratio at lift-off length along with residence time and gas temperature play an important role for soot formation in a diffusion flame. Mixing capability and bulk gas temperature are the most important parameters that influence the in-cylinder soot oxidation process. Normally, research studies of soot formation-oxidation processes have been developed under controlled and not completely representative conditions of engine operation in the field. Therefore, the main objective of this work was to develop a simplified methodology to evaluate in cylinder soot oxidation under 'real' engine conditions. In particular the impact of mixing process and bulk gas temperature on late cycle soot oxidation was evaluated. The experimental measurements were made in a production light-duty diesel engine varying those parameters that have been demonstrated in the literature as the most relevant in soot formation - oxidation processes; injection pressure, ambient density and intake air temperature. To measure soot, two color method was applied by means of an optoelectronic pyrometer. To evaluate the mixing capability a specific "tracer" Apparent Combustion Time (ACT(-1)) based on the experimental heat release and injection parameters was defined. The relationship between both parameters was used to explain the soot oxidation process. (C) 2016 Elsevier Ltd. All rights reserved.The authors acknowledge General Motors Global Research & Development for supporting this research.López, JJ.; Martín, J.; García Martínez, A.; Villalta-Lara, D.; Warey, A. (2017). Implementation of two color method to investigate late cycle soot oxidation process in a CI engine under low load conditions. Applied Thermal Engineering. 113:878-890. doi:10.1016/j.applthermaleng.2016.11.095S87889011

A Combination of Swirl Ratio and Injection Strategy to Increase Engine Efficiency

[EN] Growing awareness about CO2 emissions and their environmental implications are leading to an increase in the importance of thermal efficiency as criteria to design internal combustion engines (ICE). Heat transfer to the combustion chamber walls contributes to a decrease in the indicated efficiency. A strategy explored in this study to mitigate this efficiency loss is to promote low swirl conditions in the combustion chamber by using low swirl ratios. A decrease in swirl ratio leads to a reduction in heat transfer, but unfortunately, it can also lead to worsening of combustion development and a decrease in the gross indicated efficiency. Moreover, pumping work plays also an important role due to the effect of reduced intake restriction to generate the swirl motion. Current research evaluates the effect of a dedicated injection strategy to enhance combustion process when low swirl is used. For this purpose, a combination of theoretical (0D and 1D models) and experimental tools were used. In particular, experiments were conducted in a single-cylinder direct-injection light-duty diesel engine. The analysis also included theoretical calculations to estimate pumping losses. Results show that an increase in swirl ratio leads to an increase in the gross indicated efficiency (balancing heat transfer losses and combustion improvement) but the higher pumping losses negate this positive benefit. In the lowest swirl ratio case, a suitable injection strategy based on multiple injections, together with an increase in the injection pressure, can provide similar gross indicated efficiency as high swirl ratio case while avoiding high pumping losses.The support of GM Global R&D and the Spanish Ministry of Economy and Competitiveness (TRA2014-58870-R,) is greatly acknowledged.Olmeda, P.; Martín, J.; García Martínez, A.; Villalta-Lara, D.; Warey, A.; Doménech Llopis, V. (2017). A Combination of Swirl Ratio and Injection Strategy to Increase Engine Efficiency. SAE International Journal of Engines. 10(3):1-13. doi:10.4271/2017-01-0722S11310

An Investigation of Radiation Heat Transfer in a Light-Duty Diesel Engine

In the last two decades engine research has been mainly focused on reducing pollutant emissions. This fact together with growing awareness about the impacts of climate change are leading to an increase in the importance of thermal efficiency over other criteria in the design of internal combustion engines (ICE). In this framework, the heat transfer to the combustion chamber walls can be considered as one of the main sources of indicated efficiency diminution. In particular, in modern direct-injection diesel engines, the radiation emission from soot particles can constitute a significant component of the efficiency losses. Thus, the main of objective of the current research was to evaluate the amount of energy lost to soot radiation relative to the input fuel chemical energy during the combustion event under several representative engine loads and speeds. Moreover, the current research characterized the impact of different engine operating conditions on radiation heat transfer. For this purpose, a combination of theoretical and experimental tools were used. In particular, soot radiation was quantified with a sensor that uses two-color thermometry along with its corresponding simplified radiation model. Experiments were conducted using a 4-cylinder direct-injection light-duty diesel engine fully instrumented with thermocouples. The goal was to calculate the energy balance of the input fuel chemical energy. Results provide a characterization of radiation heat transfer for different engine loads and speeds as well as radiation trends for different engine operating conditions.Benajes Calvo, JV.; Martín Díaz, J.; García Martínez, A.; Villalta Lara, D.; Warey, A.; Doménech Llopis, V.; Vassallo, AL.... (2015). An Investigation of Radiation Heat Transfer in a Light-Duty Diesel Engine. SAE International Journal of Engines. 8(5):1-14. doi:10.4271/2015-24-2443S1148

Application of a zero-dimensional model to assess the effect of swirl on indicated efficiency

This is the author s version of a work that was accepted for publication in International Journal of Engine Research. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publication. A definitive version was subsequently published as https://doi.org/10.1177/1468087418779726[EN] Increasing internal combustion engine efficiency continues being one of the main goals of engine research. To achieve this objective, different engine strategies are being developed continuously. However, the assessment of these techniques is not straightforward due to their influence on various intermediate phenomena inherent to the combustion process, which finally result in indicated efficiency trade-offs. During this work, a new methodology to assess these intermediate imperfections on gross indicated efficiency using a zero-dimensional model is developed. This methodology is applied to a swirl parametric study, where it has been concluded that the heat transfer and the rate of heat release are the single relevant changing phenomena. Results show that heat transfer always increases with swirl affecting negatively gross indicated efficiency (around -0.5%), while the impact of combustion velocity is not monotonous. It is enhanced up to a certain swirl ratio (it changes with engine speed) at low engine speed (resulting in an increment of +1.7% in gross indicated efficiency), but it is slowed down at high engine speed with the consequent worsening of gross indicated efficiency (-0.8%).The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This work was partially funded by GM Global R&D and the Government of Spain through Project TRA2013-41348-R. D. B.-C. was partially supported through contract FPI-S2-2016-1356 of the Programa de Apoyo para la Investigacion y Desarrollo (PAID) of Universitat Politecnica de Valencia.Broatch, A.; Martín, J.; García Martínez, A.; Blanco-Cavero, D.; Warey, A.; Domenech, V. (2019). Application of a zero-dimensional model to assess the effect of swirl on indicated efficiency. 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In-cylinder soot radiation heat transfer in direct-injection diesel engines

The efficiency and CO2 are one of the main concerns of automotive manufacturers. There are several strategies under investigation to solve this problem. In the present work, the research effort has been focused on improving knowledge of in-cylinder heat transfer and its impact on engine efficiency. In particular, soot radiation was studied since it can be considered a significant source of the efficiency losses in modern diesel engines. Considering previous studies, the portion of total chemical energy released during combustion lost due to radiation heat transfer varies widely from 0.5% up to 10%, depending on engine parameters and combustion process. Thus, the main objective of this work was to evaluate the amount of energy lost to soot radiation relative to the input fuel chemical energy during the combustion event under different operating conditions in a completely controlled environment provided by an optical engine. Under these simplified conditions, two-color method was applied by using high speed imaging pyrometer with cameras (two dimensional results) and optoelectronic pyrometer (zero dimensional results). Once a detailed comparison between both diagnostics was performed, optoelectronic pyrometer was used to characterize radiant energy losses in a fully instrumented 4-cylinder direct-injection lightduty diesel engine. In particular swirl ratio, 'EGR and combustion phasing effects on radiation heat transfer were evaluated.The authors acknowledge General Motors Global R&D for supporting this research and to express their gratitude to Spanish economy and competitiveness ministry for partially funding this research under the project HiReCo TRA2014-58870-R.Benajes Calvo, JV.; Martín Díaz, J.; García Martínez, A.; Villalta Lara, D.; Warey, A. (2015). In-cylinder soot radiation heat transfer in direct-injection diesel engines. Energy Conversion and Management. 106:414-427. https://doi.org/10.1016/j.enconman.2015.09.059S41442710