Hydrogen Spark Ignition Research Articles

Optimizing hydrogen spark-ignition engine performance and pollutants by combining VVT and EGR strategies through numerical simulation

Hydrogen combustion engines are considered one of the leading solutions for decarbonizing road transport, mainly due to the possibility of adapting current engines for hydrogen operation with minor changes. This research extensively analyzes the effect of combined EGR (exhaust gas recirculation) and VVT (variable valve timing) strategies on the performance and emissions of a commercial turbocharged SI engine fueled with hydrogen. To this end, a 1D model of the said engine, widely validated for gasoline operation, was adapted to simulate the engine's behavior with hydrogen. This adaptation involved hardware changes and the implementation of a predictive hydrogen combustion submodel, previously calibrated using experimental data from a single-cylinder engine of similar geometry. Firstly, 400 hydrogen engine simulations without EGR were conducted to optimize the VVT system for fuel efficiency over a wide operating range. A detailed explanation of the causality of varying valve overlap on pumping losses, in-cylinder gas composition, and combustion is provided from these simulations. Then, a series of EGR sweeps were simulated to study its impact on performance and NOx at various degrees of load; concluding that diluting with EGR, rather than air, leads to reduced NOx emissions in exchange for slightly increased fuel consumption.

The Interaction between Short- and Long-Term Energy Storage in an nZEB Office Building

The establishment of near-autonomous micro-grids in commercial or public building complexes is gaining increasing popularity. Short-term storage capacity is provided by means of large battery installations, or, more often, by the employees’ increasing use of electric vehicle batteries, which are allowed to operate in bi-directional charging mode. In addition to the above short-term storage means, a long-term storage medium is considered essential to the optimal operation of the building’s micro-grid. The most promising long-term energy storage carrier is hydrogen, which is produced by standard electrolyzer units by exploiting the surplus electricity produced by photovoltaic installation, due to the seasonal or weekly variation in a building’s electricity consumption. To this end, a novel concept is studied in this paper. The details of the proposed concept are described in the context of a nearly Zero Energy Building (nZEB) and the associated micro-grid. The hydrogen produced is stored in a high-pressure tank to be used occasionally as fuel in an advanced technology hydrogen spark ignition engine, which moves a synchronous generator. A size optimization study is carried out to determine the genset’s rating, the electrolyzer units’ capacity and the tilt angle of the rooftop’s photovoltaic panels, which minimize the building’s interaction with the external grid. The hydrogen-fueled genset engine is optimally sized to 40 kW (0.18 kW/kWp PV). The optimal tilt angle of the rooftop PV panels is 39°. The maximum capacity of the electrolyzer units is optimized to 72 kW (0.33 kWmax/kWp PV). The resulting system is tacitly assumed to integrate to an external hydrogen network to make up for the expected mismatches between hydrogen production and consumption. The significance of technology in addressing the current challenges in the field of energy storage and micro-grid optimization is discussed, with an emphasis on its potential benefits. Moreover, areas for further research are highlighted, aiming to further advance sustainable energy solutions.

Numerical investigation on gaseous fuel injection strategies on combustion characteristics and NO emission performance in a pure hydrogen engine

With the proposal of “dual-carbon” goals and increasingly stringent emission regulations, hydrogen as a zero-carbon alternative fuel has great potential in engine applications. In the appliance of pure hydrogen engines, direct injection plus lean burn technology can effectively improve engine performance and reduce emissions. Therefore, this work establishes a three-dimensional (3D) simulation model of the pure hydrogen spark-ignition internal combustion engine (ICE) coupled with chemical reaction kinetics. Then, the applicability of different commonly used hydrogen simplified mechanisms to characterize the combustion process based on experimental data is evaluated, and the feasibility of the transient calculation model is verified. Then, the engine combustion and emission performance are compared by adopting hydrogen port injection (HPI) and hydrogen direct injection (HDI) strategies. Meanwhile, the effects of hydrogen injection timing (HIT) on flow, combustion and nitric oxide (NO) emission processes under direct injection plus lean burn mode are analyzed. The results show that: 1. For mixture distribution at ignition timing (IT), the hydrogen should be distributed near the spark plug and avoid its concentration being too rich since the richer mixture will lead to intense combustion and rapid heat release. 2. When using HDI mode, the engine combustion performance and power performance are better than that of the HPI mode. Delaying HIT, the power performance improves under HDI modes, while both the indicated thermal efficiency (ITE) and indicated mean effective pressure (IMEP) reached the maximum at Case6-HDI-100 with the values are 40.52 % and 0.498 MPa, respectively. 3. Considering the engine combustion, power and emission performance, Case6-HDI-100 (HIT at 100 °CA BTDC) is the preferred scheme. Its ITE and IMEP are 8.49 % and 37.33 % higher than that of Case1-HPI (HPI mode scheme) and 6.50 % and 14.95 % higher than that of Case4-HDI-220 (the lowest scheme under HDI mode), respectively, while nitrogen oxide (NOx) emissions meet the European Stage V non-road emission standards. This study provides some reference values for the combustion design of pure hydrogen ICEs.

Proposal and validation of a numerical framework for 3D-CFD in-cylinder simulations of hydrogen spark-ignition internal combustion engines

In the light of the recent standards proposed by the European Union in terms of CO2 emissions for the internal combustion engines, the attention is increasingly focused on e-fuels, among which the renewable-produced hydrogen. The present paper proposes a numerical methodology for 3D-CFD in-cylinder simulations of hydrogen-fuelled internal combustion engines. The proposed framework includes in-house developed models for ignition, knock and heat transfer and it is based on the G-equation combustion model. The predictive capabilities of the methodology are validated against experimental data on a single-cylinder naturally-aspirated diesel engine converted for spark-ignited hydrogen operation. Specifically, H2 is direct injected thanks to two injectors installed on the cylinder head. Moreover, a spark plug is added and the compression ratio is lowered. The investigated conditions cover different revving speeds (from 1500 rpm to 3000 rpm) and equivalence ratios (0.4, 0.6 and 0.8). The satisfying agreement between numerical results and experimental counterparts paves the way to future studies (e.g. on emission modelling) and engine optimization.

Experimental measurements of ultra-lean hydrogen ignition delays using a rapid compression machine under internal combustion engine conditions

In order to mitigate greenhouse gas and pollutant emissions from the transportation sector, the use of green e-fuels is planned. Hydrogen spark ignition engines (H2ICEs) are one of the most important technologies for reducing dependence on fossil fuels. However, these combustion engines are prone to some abnormal combustion phenomena, such as knocking, and require further investigation to get a better understanding of hydrogen combustion properties. This study used a rapid compression machine to present experimental ignition delay measurements of ultra-lean hydrogen/air mixtures under internal combustion engine conditions. The fuel–air ratio ranged from 0.2 to 0.5, the compression temperature varied from 900 to 1030 K, and the compression pressure ranged from 20 to 60 bar. A comparison with often-used and up-to-date hydrogen kinetic mechanisms was performed. The experimental results were consistent and showed an overall good agreement with numerical simulations. The impact of 2 HO2 ⇌ 2 OH + O2 addition on recent kinetic mechanisms was also investigated and presented an average decrease of 20% in ignition delay. Finally, new third-body efficiencies of H2O were evaluated and showed no impact on prediction. The aim of this approach was to provide new experimental data for kinetic mechanism validation and optimization.

Knock Mitigation and Power Enhancement of Hydrogen Spark-Ignition Engine through Ammonia Blending

Hydrogen and ammonia are primary carbon-free fuels that have massive production potential. In regard to their flame properties, these two fuels largely represent the two extremes among all fuels. The extremely fast flame speed of hydrogen can lead to an easy deflagration-to-detonation transition and cause detonation-type engine knock that limits the global equivalence ratio, and consequently the engine power. The very low flame speed and reactivity of ammonia can lead to a low heat release rate and cause difficulty in ignition and ammonia slip. Adding ammonia into hydrogen can effectively modulate flame speed and hence the heat release rate, which in turn mitigates engine knock and retains the zero-carbon nature of the system. However, a key issue that remains unclear is the blending ratio of NH3 that provides the desired heat release rate, emission level, and engine power. In the present work, a 3D computational combustion study is conducted to search for the optimal hydrogen/ammonia mixture that is knock-free and meanwhile allows sufficient power in a typical spark-ignition engine configuration. Parametric studies with varying global equivalence ratios and hydrogen/ammonia blends are conducted. The results show that with added ammonia, engine knock can be avoided, even under stoichiometric operating conditions. Due to the increased global equivalence ratio and added ammonia, the energy content of trapped charge as well as work output per cycle is increased. About 90% of the work output of a pure gasoline engine under the same conditions can be reached by hydrogen/ammonia blends. The work shows great potential of blended fuel or hydrogen/ammonia dual fuel in high-speed SI engines.

1D/3D simulation procedure to investigate the potential of a lean burn hydrogen fuelled engine

In recent years hydrogen, especially the one generated by renewable energy, is gaining increasing attention as a clean fuel to support the future mobility towards efficient and low emission solutions for propulsion systems. In this scenario, the present work deals with the virtual conversion of a single-cylinder Diesel engine, conceived for marine applications, into a hydrogen Spark Ignition (SI) unit. A simulation methodology is adopted, combining 1D and 3D Computational Fluid Dynamics (CFD) methods. First, experiments are realized on the original Diesel engine mounted on a test bench, collecting main performance indicators and emissions. A complete 1D engine model (GT-Power™) is developed and validated against measurements. Then, a 3D model of the cylinder (STAR-CD) is set-up and the related combustion outcomes are compared both with 1D and experimental results, showing an overall good agreement. In the second stage, the Diesel unit is converted into a port-injected hydrogen SI engine; the 3D model is re-arranged and utilized to reproduce pre-mixed hydrogen combustions under ultra-lean air/fuel (A/F) mixtures. Also, the 1D model is partly modified and coupled to an advanced combustion sub-model integrated with fast tabulated chemical kinetics to predict the knock. In particular, 1D combustion evolution is calibrated against the results of 3D CFD hydrogen combustion simulation. Finally, the calibrated 1D model is applied to investigate the advantages of ultra-lean hydrogen combustion in terms of efficiency, NO, and unburned H2 formation at medium/high loads.

Analysis of the exhaust hydrogen characteristics of high-compression ratio, ultra-lean, hydrogen spark-ignition engine using advanced regression algorithms

• Exhaust H 2 and NO x were investigated using heavy-duty, hydrogen spark-ignition engine. • Lower excess air ratio exhibited lower H 2 emission, but greater heat transfer loss. • The regression model achieved a high accuracy under various operating conditions. • The proposed H 2 emission model is applicable to various HICEs. Hydrogen is a leading alternative fuel for eliminating the carbon emissions of internal combustion engines. Moreover, the use of hydrogen improves the combustion owing to its high flame speed. The hydrogen selective catalytic reduction is a promising solution for the reduction of nitric oxides (NOx), which is the sole regulated gas species in hydrogen-fueled internal combustion engines. In the present study, hydrogen and NOx emissions, the crucial species for the catalyst performance, were investigated using a heavy-duty, hydrogen spark-ignition engine. The ratio of H 2 to NOx was above 100 at the excess air ratio (lambda) of 2.5 or higher. Three-dimensional, numerical simulation showed that the in-cylinder hydrogen distribution was dependent on the engine load and the lambda value. A regression analysis showed that the exhaust hydrogen quantity had a strong correlation with the seven parameters, namely engine speed, the gross indicated effective pressure (IMEPg), lambda, spark timing, total combustion duration, peak in-cylinder temperature, and peak pressure rise rate. Among these parameters, the IMEPg and the lambda value exhibited the highest weights in a neighborhood component analysis. The regression model with the seven features exhibited the highest R 2 value of 0.94 with the squared exponential Gaussian process regression. The proposed prediction model can contribute to not only reducing NOx emission with aftertreatment, but also maximizing the thermal efficiency of hydrogen-fueled internal combustion engines.

Multi-dimensional modeling of mixture preparation in a direct injection engine fueled with gaseous hydrogen

With the recent advances of direct injection (DI) technology, introducing hydrogen into the combustion chamber through DI is being considered as a viable approach to circumvent backfire and pre-ignition encountered in early generations of hydrogen engines. As part of a broader vision to develop a robust numerical model to study hydrogen spark ignition (SI) combustion in internal combustion (IC) engines, the present numerical investigation focuses on mixture preparation in a hydrogen DI SI engine. This study is carried out with a single hole injector with gaseous hydrogen injected at 100 bar injection pressure. Simulations are carried out for high and low tumble configurations and validated against optical data acquired from planar laser induced fluorescence (PLIF) measurements. Varying mesh configurations are investigated for the impact on in-cylinder mixture distribution. A particular emphasis is placed on the effect of nozzle geometry and mesh orientation near the wall. Overall, the computational model is found to predict the mixture distribution in the combustion cylinder reasonably well. The results showed that the alignment of mesh with the flow direction is important to achieve good agreement between numerical analysis and optical measurement data.

High pressure direct injection of gaseous fuels using a discrete phase methodology for engine simulations

Direct gaseous fuel injection in internal combustion engines is a potential strategy for improving in-cylinder combustion processes, performance and emissions outputs and, in the case of hydrogen, could facilitate a transition away from fossil fuel usage. Computational fluid dynamic studies are required to fully understand and optimise the combustion process, however, the fine grids required to adequately model the underexpanded gas jets which tend to result from direct injection make this a difficult and cumbersome task. In this paper the gaseous sphere injection (GSI) model, which utilises the Lagrangian discrete phase model to represent the injected gas jet, is further improved to account for the variation in the jet core length with better estimation due to total pressure ratio change. The improved GSI model is then validated against experimental hydrogen and methane underexpanded freestream jet studies, mixing in a direct injection hydrogen spark ignition engine and combustion in a pilot ignited direct injection methane compression ignition engine. The improved GSI model performs reasonably well across all cases examined which cover various pressure ratios, injector diameters, injection conditions and disparate gases (hydrogen and methane) while also allowing for relatively coarse meshes (cheaper computational cost) to be used when compared to those needed for fully resolved modelling of the gaseous injection process. The improved GSI model should allow for efficient and accurate investigation of direct injection gaseous fuelled engines.

Effect of turbocharger on performance and thermal efficiency of hydrogen-fueled spark ignition engine

This study systematically investigated the application of a turbocharger system to a hydrogen spark ignition engine to extend operating limitations under high loads. The exhaust system of a commercial 2.4-L natural aspiration spark ignition engine was modified by adopting a turbocharger system. Engine test speeds were 2000–6000 rpm at intervals of 1000 rpm. The intake pressure was fixed for each experimental case, however, the quantity of hydrogen and spark advance timings were varied before the back-fire occurred. High load conditions under natural aspiration and turbocharging conditions were compared. The results indicated that distinctly higher boosts with the turbocharging system helped extend high load conditions, however, the high exhaust pressure obstructed the increasingly high load conditions under high speeds.

Local fuel concentration measurement through spark-induced breakdown spectroscopy in a direct-injection hydrogen spark-ignition engine

Quantitative measurements of local fuel concentrations were conducted in a direct-injection hydrogen spark-ignition research engine using the spark-induced breakdown spectroscopy (SIBS) technique. For SIBS measurements, a new sensor was developed from a commercially available M12-type spark plug with no major modifications to the electrodes. The new plug sensor showed better durability and required less maintenance when used in a hydrogen research engine. Emission spectra from the plasma generated by the spark plug were collected through an optical fibre housed in the centre electrode of the plug and resolved spectrally for atomic emissions of Hα, O(I), and N(I). The main focus of the present work was to characterise the effects of ambient pressure at ignition timing on spectral line emissions and to improve the accuracy of SIBS measurements by taking into account the pressure dependency of atomic emissions. A significant effect of the corresponding pressure at ignition timing was observed on spark-induced breakdown spectroscopic measurements and emission line characteristics. Retarded spark timing (i.e. higher ambient pressure at the ignition site) resulted in lower spectral line intensities as well as weaker background emissions. It is well established that with relatively higher pressure and density of atoms or molecules, the cooling of expanding plasma accelerates, and the collision probability increases, leading to both a weaker broadband continuum and atomic emissions. A “calibration MAP” representing the correlation of air excess ratio (relative air/fuel ratio) with both intensity ratio and pressure at ignition timing was created and subsequently used for quantitative measurements of local fuel concentrations for both port injection and direct injection strategies to demonstrate and explore the effects of pressure dependency of atomic emission on the accuracy of the SIBS measurements. Local stratification of the fuel mixture in the vicinity of the spark gap location associated with direct injection strategies was confirmed; the coefficient of variation of the local air excess ratio was relatively small for measurements made using the calibration map. This demonstrated that the measurement accuracy of local fuel concentrations through a spark plug sensor can be improved significantly when the pressure dependency of atomic emissions is taken into account.

Investigating the effect of the heat transfer correlation on the predictability of a multi-zone combustion model of a hydrogen-fuelled spark ignition engine

Research on the heat transfer in hydrogen-fuelled spark ignition engines indicates that the two most common heat transfer correlations, namely the Annand correlation and the Woschni correlation, cannot perfectly predict the heat flux during the engine cycle. This questions the accuracy of thermodynamic hydrogen engine models because the heat transfer is one of the important submodels in the development of a thermodynamic model. In addition, the Hohenberg correlation and the Shudo–Suzuki correlation have not been evaluated for hydrogen engines. In this study, a thermodynamic model of the closed cycle of a spark ignition engine is developed with a multi-zone combustion submodel to predict the pressure and the heat flux traces and to compare the predicted values with the available experimental results. The effects of implementing different heat transfer correlations in the prediction of the maximum pressure of the cycle, the total heat transfer and the work are presented for two different compression ratios and two equivalence ratios with different ignition timings. The results indicated that, although the implemented heat transfer correlations predicted the heat flux and the heat transfer with a large percentage error, the fractal-based combustion model implementing the Annand correlation and the Shudo–Suzuki correlations predicted the maximum pressure and the total work with less than 10% error. Finally, a modified version of the Hohenberg correlation for predicting the total heat transfer in a hydrogen spark ignition engine was presented.

An investigation on effect of in-cylinder swirl flow on performance, combustion and cyclic variations in hydrogen fuelled spark ignition engine

This study investigates how engine performance, cyclic variations and combustion parameters are affected by swirling flow in hydrogen spark ignition (SI) engine. Swirling flow was produced in the cylinder during the induction stroke by intake port having entry angles of 0°, 10°, 20° and 30°. In addition, tumble angle of 8° was positioned for given entry angles. The engine was operated under lean mixture (ϕ = 0.6) conditions and engine speeds of 1400, 1600 and 1800 rpm. As a result, it was found that swirling flow enhances performance of hydrogen SI engine around 3% when operating engine with entry angle of 20°. The combustion duration and the cyclic variation in hydrogen SI engine can be reduced with optimum swirling flow. The stability of combustion in hydrogen SI engine is mainly dependent on cyclic variations in the flame initiation period and the cyclic variations in this period can be reduced with controlled swirling flow.

A correlation for the laminar burning velocity for use in hydrogen spark ignition engine simulation

Hydrogen is an interesting fuel for internal combustion engines. It is a versatile fuel that enables high efficiencies and low emissions of oxides of nitrogen (NO x), throughout the load range. Computer simulations of hydrogen-fuelled spark ignition engines would facilitate the development of these engines. These necessitate the calculation of the turbulent combustion of hydrogen to track the flame propagation throughout the combustion chamber and resolve in-cylinder pressure and temperature. In order to do this, the laminar burning velocity of the in-cylinder mixture at the instantaneous pressure and temperature is needed. However, there is a scarcity of data in the literature, particularly at engine conditions. This is further complicated by the occurrence of flame instabilities at engine-like pressures, which compromises some of the existing data. This paper discusses the available experimental data and correlations for the laminar burning velocity of hydrogen mixtures, and their deficiencies. One-dimensional chemical kinetic calculations of the laminar burning velocity of mixtures of hydrogen, air and residuals, at engine-like pressures and temperatures are then reported. A correlation is derived for use in hydrogen engine codes and is compared to other correlations presented previously.

Evaluation of a combustion model for the simulation of hydrogen spark-ignition engines using a CFD code

The present work deals with the evaluation of a combustion model that has been developed, in order to simulate the power cycle of hydrogen spark-ignition engines. The motivation for the development of such a model is to obtain a simple combustion model with few calibration constants, applicable to a wide range of engine configurations, incorporated in an in-house CFD code using the RNG k– ɛ turbulence model. The calculated cylinder pressure traces, gross heat release rate diagrams and exhaust nitric oxide (NO) emissions are compared with the corresponding measured ones at various engine loads. The engine used is a Cooperative Fuel Research (CFR) engine fueled with hydrogen, operating at a constant engine speed of 600 rpm. This model is composed of various sub-models used for the simulation of combustion of conventional fuels in SI engines; it has been adjusted in the current study specifically for hydrogen combustion. The basic sub-model incorporated for the calculation of the reaction rates is the characteristic conversion time-scale method, meaning that a time-scale is used depending on the laminar conversion time and the turbulent mixing time, which dictates to what extent the combustible gas has reached its chemical equilibrium during a predefined time step. Also, the laminar and turbulent combustion velocity is used to track the flame development within the combustion chamber, using two correlations for the laminar flame speed and the Zimont/Lipatnikov approach for the modeling of the turbulent flame speed, whereas the (NO) emissions are calculated according to the Zeldovich mechanism. From the evaluation conducted, it is revealed that by using the developed hydrogen combustion model and after adjustment of the unique model calibration constant, there is an adequate agreement with measured data (regarding performance and emissions) for the investigated conditions. However, there are a few more issues to be resolved dealing mainly with the ignition process and the applicability of a reliable set of constants for the emission calculations.

Visualization of auto-ignition and pressure wave during knocking in a hydrogen spark-ignition engine

Visualizations of auto-ignition inside the end-gas region due to flame propagation and pressure waves that occur during knocking were carried out in a hydrogen spark-ignition engine using a high-speed camera. Our results demonstrated that auto-ignition in an end-gas region that was compressed by the propagating flame front could be visualized using the high-speed color camera. A large amount of unburned mixture caused by the auto-ignited kernel explosion generated the strong pressure waves. Strong pressure wave oscillations induced by the initial auto-ignition could be visualized using a video camera with a speed of 250 kframes/s. The auto-ignition and pressure waves caused the thermal boundary layer to breakdown near the cylinder wall and piston head, therefore combustion of the lubricant oil grease was visible inside burned gas region. This auto-ignition and pressure waves may result in damage to the cylinder wall and piston head during engine knocking.

Spark-Ignition and Combustion Characteristics of High-Pressure Hydrogen and Natural-Gas Intermittent Jets

Recently, an in-cylinder injection method has been considered for the improvement of thermal efficiency in natural-gas and hydrogen spark-ignition (SI) engines. However, the SI and combustion processes of gaseous jets are not well understood. The present study aims to provide fundamental data for the development of direct-injection SI gas engines. The ignition, combustion, and flame behavior of high-pressure and intermittent hydrogen and natural-gas jets in a constant volume combustion chamber were investigated. The effects of injection pressure, nozzle size, ambient pressure, and spark location were also investigated for various spark timings and equivalence ratios.

Efficiency of Advanced Ground Transportation Technologies

This paper presents thermodynamic analyses of ten different scenarios for using natural gas to power motor vehicles. Specifically, it presents a comparison between different types of automotive vehicles using fuels made from natural gas feedstock. In comparing the various fuel-vehicle options, a complete well-to-wheel fuel cycle is considered. This approach starts with the well at which the feedstock is first extracted from the ground and ends with the power finally delivered to the wheels of the vehicle. This all-inclusive comparison is essential in order to accurately and fairly compare the transportation options. This study indicates that at the present time hybrid-electric vehicles, particularly those using diesel components, can achieve the highest efficiency among available technologies using natural gas as the primary energy source. Hydrogen spark ignition, all-electric battery-powered, and methanol fuel cell vehicles rank lowest in well-to-wheel efficiency because of their poor fuel production efficiencies.