Potential of water direct injection in a CAI/HCCI gasoline engine to extend the operating range towards higher loads

[EN] CAI (Controlled AutoIgnition) systems, also named HCCI (Homogeneous Charge Compression Ignition), are a promising way to improve gasoline engines. This combustion mode is more efficient than the standard SI (Spark Ignition) combustion and, additionally, it has very low emissions, especially NOx emissions, which represent a source of problems nowadays. The main problem of this combustion mode is the constrained operating range, caused, on the one hand, by the difficulty to ignite the fuel since it has to be auto-ignited by the control of the mixture reactivity, and, on the other hand, by its high heat release rates, causing high pressure gradients and, in some circumstances, knocking combustion. In this paper, the possibility to use directly injected water into the combustion chamber as a reactivity suppressor in order to extend the constrained load range of CAI operation is evaluated. For this study, a four-stroke single-cylinder gasoline engine has been modified to allow CAI combustion by means of adapted valve trains enabling to keep hot residual gases inside the cylinder, which will provoke the fuel autoignition. Additionally, a water direct injection system has been installed in the engine to carry out this study. The results show that water injection is an efficient strategy to increase the maximum affordable load in CAI conditions, since the reactivity of the mixture can be suitably controlled, thus reducing the pressure gradients and the knocking tendency of the combustion process, also keeping good levels of combustion stability. Nevertheless, the engine has to be significantly boosted and the necessary intake pressure compared to a conventional SI operation mode in stoichiometric conditions is much higher.The research was performed as part of the Research Unit (Forschergruppe) FOR 2401 "Optimization based Multiscale Control for Low Temperature Combustion Engines", which is funded by the German Research Association (Deutsche Forschungsgemeinschaft, DFG). The support is gratefully acknowledged. The authors would like to thank also different members of the VKA institute for combustion engines of the RWTH Aachen university and CMT-Motores Termicos team of the Universitat Politecnica de Valencia for their contribution to this work and also thank the Universitat Politecnica de Valencia (contract 3102) and the Spanish Ministry of Economy and Competitiveness (contract BES-2016-077610) for financing the PhD. studies of Jorge Valero-Marco, partly funded by FEDER and the Spanish Government through project TRA2015-67136-R.Valero-Marco, J.; Lehrheuer, B.; López, JJ.; Pischinger, S. (2018). Potential of water direct injection in a CAI/HCCI gasoline engine to extend the operating range towards higher loads. Fuel. 231:317-327. https://doi.org/10.1016/j.fuel.2018.05.093S31732723

Effect of engine operating parameters on space- and species-resolved measurements of engine-out emissions from a single-cylinder spark ignition engine

The development and validation of detailed simulation models of in-cylinder combustion, emission formation mechanisms and reaction kinetics in the exhaust system are of crucial importance for the design of future low-emission powertrain concepts. To investigate emission formation mechanisms on one side and to create a solid basis for the validation of simulation methodologies (e.g. 3D-CFD, multi-dimensional in-cylinder models, etc.) on the other side, specific detailed measurements in the exhaust system are required. In particular, the hydrocarbon (HC) emissions are difficult to be investigated in simulation and experimentally, due to their complex composition and their post-oxidation in the exhaust system. In this work, different emission measurement devices were used to track the emission level and composition at different distances from the cylinder along the exhaust manifold, from the exhaust valve onwards. A fast-FID (FFID) was used to measure the cycle-resolved total-HC (THC) emissions and an ion molecule reaction mass-spectrometer (IMR-MS) to determine the average concentration of some selected HC components. Conventional exhaust analyzers were used additionally to measure the average levels of the important exhaust gas components (THC, NOx, CO, CO2, O2). The measurements were conducted on a 0.4 l single-cylinder spark-ignited (SI) research engine. The effects and cross-effects on emissions of several relevant operating parameters were evaluated. Different result patterns are observed in the different measuring positions. In this work, selected results on the effect of air-to-fuel ratio and spark timing are presented. For the air-fuel-ratio variation, the FFID results show that the THC quenching increases with lean operating condition and the IMR-MS that this increase corresponds to an increase in fuel-HC and a reduction in non-fuel-HC. In the spark timing variation, the trends of THC in the exhaust port and in the exhaust runner suggest the presence of HC oxidation in the exhaust port, due to higher exhaust temperature with retarded combustion. Additionally, the IMR-MS confirm the presence of late and incomplete oxidation with the increase of non-fuel species.</p

Study of the engine configuration effect on the maximum achievable load in CAI using water injection

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/10.1177/1468087420960858.[EN] The approach of this research is to enlarge the knowledge about the methodologies to increase the maximum achievable load degree in the context of gasoline CAI engines. This work is the continuation of a previous work related to the study of the water injection effect on combustion, where this strategy was approached. The operating strategies to introduce the water and the interconnected settings were deeply analyzed in order to optimize combustion and to evaluate its potential to increase the maximum load degree when operating in CAI. During these initial tests, the engine was configured to enhance the mixture autoignition. The compression ratio was high compared to a standard gasoline engine, and suitable fuel injection strategies were selected based on previous studies from the authors to maximize the reactivity of the mixture, and get a stable CAI operation. Once water injection proved to provide encouraging results, the next step dealt in this work, was to go deeper and explore its effects when the engine configuration is more similar to a conventional gasoline engine, trying to get CAI combustion closer to production engines. This means, mainly, lower compression ratios and different fuel injection strategies, which hinders CAI operation. Finally, since all the previous works were performed at constant engine speed, the engine speed was also modified in order to see the applicability of the defined strategies to operate under CAI conditions at other operating conditions. The results obtained show that all these modifications are compatible with CAI operation: the required compression ratio can be reduced, in some cases the injection strategies can be simplified, and the increase of the engine speed leads to better conditions for CAI combustion. Thanks to the analysis of all this data, the different key parameters to manage this combustion mode are identified and shown in the paper.The author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This research work was part of the Research Unit (Forschergruppe) FOR 2401 Optimization based Multiscale Control for Low Temperature Combustion Engines, funded by the German Research Association (Deutsche Forschungsgemeinschaft, DFG). The support for this research is gratefully acknowledged.Valero-Marco, J.; Lehrheuer, B.; López, JJ.; Pischinger, S. (2021). Study of the engine configuration effect on the maximum achievable load in CAI using water injection. International Journal of Engine Research. 22(9):2945-2957. https://doi.org/10.1177/1468087420960858S29452957229Onishi, S., Jo, S. H., Shoda, K., Jo, P. D., & Kato, S. (1979). 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