Tumble and swirl flow motion effects on hydrogen combustion and NOx formation in spark-ignition engines for passenger car engines J. Valero-Marco, J. Martín, S. Molina, M. Olcina-Girona, D. Gessaroli, F.C. Pesce International Journal of Hydrogen Energy, 2026 This study presents an experimental comparison of three in-cylinder flow strategies — tumble, swirl, and flat deck swirl (FD swirl) — in a hydrogen-fueled spark-ignition engine under lean operation. Two single-cylinder direct-injection research engines were used to represent tumble and swirl architectures, with a modified swirl configuration to obtain FD swirl. Three representative operating points at fixed lambda, comb phasing, and load degree were evaluated, after optimizing valve timing, injection phasing, and spark timing. The analysis focused on burn rate, combustion stability, knock tendency, thermal efficiency, and emissions (NO x and unburned H 2 ). Tumble delivered the fastest and most stable combustion, lowest knock intensity, and highest efficiency (up to 47%, compared to 38% for swirl). FD swirl showed intermediate behavior, which improved combustion relative to swirl. However, tumble produced higher NO x at high load and increased unburned H 2 . The results clarify how flow topology governs hydrogen combustion and provides empirical guidelines for the conversion from previous specialized designs to high-efficiency hydrogen engine development. • Tumble flow presents a faster and most stable H 2 combustion. • Tumble reduces knock intensity via shorter end-gas residence time. • Thermal efficiency ranked: Tumble >FD swirl > Swirl. • FD swirl offers best compromise between efficiency and emissions. • Swirl architecture shows limitations for SI hydrogen operation.
Study of the engine configuration effect on the maximum achievable load in CAI using water injection J Valero-Marco, B Lehrheuer, JJ López, S Pischinger International Journal of Engine Research, 2021 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.
Characterization of the turbulent flame front surface in spark ignition engines during spark ignition operation to identify controlled auto-ignition and abnormal combustion Vicente Macián, J. Javier López, Jaime Martín, Jorge Valero-Marco International Journal of Engine Research, 2021 The combustion diagnostics and subsequent analysis are standardized tools based on the estimation of the heat release law (HRL). From this estimation, the different combustion parameters can be obtained: combustion phasing and duration, heat release rate, and so on. This analysis might be usually enough to study traditional spark ignition (SI) engines. However, with the new upcoming SI engines, this is probably not the case anymore, since different combustion modes can be operated in the same engine, as for instance a combination of SI and controlled auto-ignition (CAI) combustion modes. When different combustion modes are combined, it seems interesting to study in more depth the HRL, trying to get more data and to study the differences among the diverse combustion modes. Toward this end, a methodology to go deeper in the study of the HRL is proposed in this work, consisting of, mainly quantifying and taking into account the most relevant influencing parameters: the fuel properties (mainly its lower heating value), the in-cylinder oxygen content, the density of the burned and unburned zones, the laminar combustion speed, and the turbulence effect. With the proposed methodology, a standard SI combustion, developed by a flame front, can be characterized at any given operating point. This would allow to predict which the combustion developement would be, at this operating point, assuming it to be developed by a flame front. Subsequently, this SI combustion prediction can be compared to the one obtained experimentally, making it possible to identify and analyze abnormal combustion phenomena, as well as to study the differences between a combustion developed by a flame front (SI) and by auto-ignition (CAI). Derived from this work, an alternative equation to experimentally characterize the laminar combustion velocity has also been proposed, in order to improve its applicability in a wider range of fuel/air ratios and dilution degrees.
Evaluation of the Potential Benefits of an Automotive, Gasoline, 2-Stroke Engine J. Javier Lopez, Ricardo Novella, Jorge Valero-Marco, Gilles Coma, Frederic Justet SAE Technical Papers, 2015 <div class="section abstract"><div class="htmlview paragraph">In the present paper, the use of a 2-stroke (2S) concept in an automotive gasoline engine is evaluated. In a first stage, the engine architecture chosen is discussed. Taking into account the requirements in gas exchange processes, a uniflow scavenging design was retained (intake ports in the cylinder, controlled by the piston; exhaust valves in the cylinder head, controlled by a Variable Valve Timing, VVT, system), performed by an external blower driven by the crankshaft. To avoid any fuel short-circuiting and to keep an acceptable cost, a direct injection (DI) air-assisted fuel injection system was selected. Since the engine behavior is much more complex compared to a classical 4-stroke engine, some complexity in the engine design needs to be added to allow engine optimization at the different operating conditions. This is the main reason why a VVT system, as well as a flexible fuel injection system were selected.</div><div class="htmlview paragraph">In a second stage, the chosen engine concept is evaluated. At high loads, because of the high quality of the scavenging process, the combustion initiation is controlled by a spark as in any standard spark ignition (SI) engine. However, at low load, the scavenging process is incomplete, and the high amount of residual gases leads, in some cases, to a controlled autoignition (CAI) combustion process. These two completely different scenarios are analyzed in the paper. In summary, on the one hand, the operation under SI conditions is basically similar to that of any classical 4-stroke, SI engine, but with higher knock risk. On the other hand, the operation in CAI leads to a faster combustion process, which might lead to higher fuel efficiency. However the control of the combustion process is more complex, since it is more sensitive to the operating parameters (air temperature, combustion chamber walls temperature…), and not fully controlled by the spark anymore. A significant effort has been carried out in the paper to understand how the combustion process can be controlled, and some ideas for such control are proposed and discussed.</div></div>
