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<div class="section abstract"<div class="htmlview paragraph"Ammonia, which is considered as an excellent hydrogen carrier, could potentially become a clean fuel for direct use in ICE.</div<div class="htmlview paragraph"An experimental setup with a strongly modified inline four-cylinder (I4) heavy duty Diesel engine was used to study different combustion modes of ammonia in ICE. The fourth cylinder of that engine was operated in a monovalent mode using either OME or Diesel fuel. Its complete exhaust stream was fed into the first cylinder of the same engine, which was operated on a dual-fuel mode by utilizing ammonia port injection and OME or Diesel pilot injection to ignite the mixture. The fourth cylinder of the I4 heavy duty engine can be operated at conditions between idle and full load and at different stoichiometries (λ) to impact both the temperature and the oxygen concentration at the exhaust of that cylinder. Since the first cylinder is fed by the complete exhaust stream of the fourth, the intake conditions of the first cylinder can be controlled appropriately and various ammonia combustion modes can be realized.</div<div class="htmlview paragraph"Emissions measurements at the intake and the exhaust of the first cylinder at different speeds and loads show the impact of the different combustion modes, especially due to temperature and oxygen content variations, on NOx and combustion efficiency. Chemical kinetics calculations have been elaborated to explain some of the main observations.</div</div
Despite the public debate nowadays on the future of Internal Combustion Engines (ICE), which is impeding their development, one limitation towards further optimization of ICE in terms of fuel consumption and emissions can be seen in the current approach and more specifically in the transient engine operation and its control. The main drawbacks in the current approach source from: 1) complex structure of mechanization including sensors and actuators, 2) low time resolution and accuracy of sensing (cost driven), 3) complex Electronic Control Unit (ECU)-software architecture associated with huge calibration effort and 4) recently, funded research due to unsecure business model of ICE is becoming less. To overcome these difficulties unexploited potential should be utilized. Some of this potential lies in cycle-by-cycle and cylinder-by-cylinder accurate fuel and air control, and in the development of physical based virtual sensors with high time resolution and accuracy. One of the main motivations for this study was to develop a measurement technique that enables crank-angle resolved air mass flow rate measurements during engine operation in a dynamometer test cell. The measurement principle is quite simple and is based on gauging the dynamic pressure in both the intake and exhaust duct at the closest possible positions to the valves. To fulfill these requirements aerodynamic probes have been developed and manufactured utilizing 3D printing. The probes have been integrated in special developed flanges, which correspond exactly to the shape of the air channels in the cylinder head of the engine. Hence, they can be mounted either in front of the valves at the intake or behind the valves at the exhaust duct. Results at different engine operating conditions have been obtained, analyzed and correlated to other sensors like air-flow meter. Those post-processed results can be further used to validate 1-D gas exchange models, or 3-D Computational Fluid Dynamics (CFD) port flow models. The ultimate scope of these measurements is to calibrate fast physical-based gas exchange models that can be directly used in the engine control framework on an embedded system.
Harmful NOx emissions generated during rapid changes in engine’s speed and load (such as acceleration or deceleration) are strongly linked to deviations in air-to-fuel ratio (λ) from its optimal setpoint. These deviations arise under transient conditions due to several factors, including sensor resolution limitations, time delays between actuators and sensors, and inaccurate air mass estimation within the engine management system.
While fuel mass control has significantly improved over the past three decades - achieving superior performance in terms of both dynamics and accuracy through the use of multiple injections per engine cycle - the primary challenge remains the precise control of air mass, particularly under transient conditions. Nonlinear wave dynamics and the inertia of the engine’s air path make traditional solutions, such as slow and inefficient actuators like the butterfly valve, inadequate.
This paper introduces a novel methodology to address these limitations by developing a device that is an order of magnitude faster than a butterfly valve while minimizing flow losses. The design philosophy is outlined, and the flow bench setup used to evaluate the performance of an instrumented prototype is presented. High-frequency data collected during testing are analyzed, and the extracted flow structure and turbulence parameters are discussed.
Finally, the dynamic performance of the newly developed device is incorporated into a transient gas exchange engine model, where its capability to control λ on a cycle-resolved basis is evaluated against a conventional throttle body. Numerous studies have proven that NOx spikes during engine’s accelerations and decelerations are well correlated to λ deviations from its setpoint. The assessment of the emissions reduction strategy under transient conditions is based on the device's precision in managing λ during each engine cycle, as derived from the transient model output.
Over the last decade, the prevailing demand for renewable energy sources initiated the electrification of the transportation sector, with the development of H2 engines and fuel cell powertrains increasingly gaining momentum alongside battery electric vehicles. One of the essential tasks to optimize the overall efficiency of these drives is to precisely, dynamically and frictionless meter the reacting gases into the conversion chambers. In this paper, we propose a novel dosing system, focusing on gases (air), that is based on the principle of a variable Venturi nozzle, which incorporates a device for rapid variation of the effective flow cross-sectional area (EA) with negligible pressure losses. Each EA corresponds to a demanded load or mass flow and thus enables a dynamic control of the stoichiometry (l) of the machine. Our patented technology mainly consists of two surfaces perpendicular to the flow direction where one is fixed in space and the other one is moving at high frequency (> 20 Hz) towards or against the flow direction. Firstly, the underlying design philosophy and the details of the first prototype are presented, followed by an extensive description of the test bench setup, including data acquisition system. This is succeeded by a thorough analysis of the high-frequency data to extract flow characteristics and turbulence parameters. Subsequently, the transient performance of the Venturi system is experimentally compared with that of a throttle body. Finally, the capability of the Venturi system to precisely control the cycle-resolved air-fuel ratio of a hydrogen engine is demonstrated through transient simulation results based on a class B car operating under the FTP-75 driving cycle.