Design Of Combustion Systems Research Articles

Prediction of gross calorific value of solid fuels from their proximate analysis using soft computing and regression analysis

ABSTRACT The determination of gross calorific value (GCV) of solid fuel is important because GCV is frequently required in the design of most combustion and other thermal systems. However, experimental determination of GCV is time-consuming, which necessitated the development of different empirical equations to estimate GCV using the elemental composition of the solid fuels. With the growing popularity of empirical equations for estimation of GCV of solid fuels, there is a need to develop reliable and suitable models for the prediction of GCV of coal from the South African coalfields (SAC). In this study, empirical models were developed to determine the relationship between the proximate analysis of coal with its GCV, using soft computing and regression analyses. A total of 32 coal samples were used to develop three empirical models based on soft computing techniques, namely; adaptive neuro-fuzzy inference system (ANFIS), artificial neural networks (ANN), and regression analysis using multilinear regression (MLR). The performances of the proposed models were evaluated using coefficient of determination (R2), mean absolute percentage error (MAPE), mean squared error (MSE) and variance accounted for (VAF). The R2, MAPE, MSE and VAF for the ANFIS are 99.92%, 2.0395%, 0.0778 and 99.918% while for the ANN, they are 99.71%, 2.863%, 0.2834 and 99.703%. The R2, MAPE, MSE and VAF for the MLR are 99.46%, 3.551%, 0.5127 and 99.460%. From the soft computing and regression analysis studies conducted, the ANFIS was found as the most suitable model for predicting the GCV for these coal samples.

Balancing Hydraulic Flow and Fuel Injection Parameters for Low-Emission and High-Efficiency Automotive Diesel Engines

<div class="section abstract"><div class="htmlview paragraph">The introduction of new light-duty vehicle emission limits to comply under real driving conditions (RDE) is pushing the diesel engine manufacturers to identify and improve the technologies and strategies for further emission reduction. The latest technology advancements on the after-treatment systems have permitted to achieve very low emission conformity factors over the RDE, and therefore, the biggest challenge of the diesel engine development is maintaining its competitiveness in the trade-off “CO<sub>2</sub>-system cost” in comparison to other propulsion systems. In this regard, diesel engines can continue to play an important role, in the short-medium term, to enable cost-effective compliance of CO<sub>2</sub>-fleet emission targets, either in conventional or hybrid propulsion systems configuration. This is especially true for large-size cars, SUVs and light commercial vehicles.</div><div class="htmlview paragraph">In this framework, a comprehensive approach covering the whole powertrain is of primary importance in order to simultaneously meet the performance, efficiency, noise and emission targets, and therefore, further development of the combustion system design and injection system represent important levers for additional improvements. For this purpose, a dedicated 0.5 dm<sup>3</sup> single-cylinder engine has been developed and equipped with, a state-of-the-art Euro 6 combustion system, and an advanced common rail fuel injection system (FIS) offering higher flexibility in terms of injection strategy and higher quantity accuracy. Three injector nozzles with different hydraulic flow rates (HF) have been selected and employed for the overall combustion process optimization.</div><div class="htmlview paragraph">The optimization has been performed by means of an extensive DoE-based test campaign in which the engine and FIS operating parameters have been parametrized with the aim to carry out a proper combination in terms of HF and injection strategy. The results at partial load conditions evidence significant advantages in applying an advanced injection pattern, while the HF reduction can significantly improve the smoke emission and combustion noise without fuel consumption penalties. Therefore, a proper combination and optimization of the HF and injection strategy can provide low noise and engine-out smoke while maintaining the rated power performance targets.</div></div>

Modelling and validation of biomass combustion in a screw burner

A combined 1D-fuel-bed and 3D-CFD model for the simulation of an innovative 35 kW screw burner has been developed and validated with experiments. The 1D-fuel-bed model is a further development of a previously presented walking column approach and accounts for the special transport conditions in a screw burner. A new reduced chemical mechanism combined with the Eddy Dissipation Concept (EDC) combustion model is used in the subsequent 3D-CFD simulation. Detailed and reduced mechanisms are first compared in an opposed jet burner and then an improved reduced chemistry model is used in CFD calculations to investigate the influence of different primary and secondary air settings and to be validated with experimental data from a 35 kW prototype burner. The model enables a reasonable prediction of the trends of variations of the excess air ratio in the primary zone (primary λ) and of the global excess air on the emissions and the heat output and is therefore suitable for the design of biomass combustion systems with a moving fuel bed.

Effects of fuel compositions on the heat generation and emission of syngas/producer gas laminar diffusion flame

Demand for the clean and sustainable energy encourages the research and development in the efficient production and utilisation of syngas for low-carbon power and heating/cooling applications. However, diversity in the chemical composition of syngas, resulting due to its flexible production process and feedstock, often poses a significant challenge for the design and operation of an effective combustion system. To address this, the research presented in this paper is particularly focused on an in-depth understanding of the heat generation and emission formation of syngas/producer gas flames with an effect of the fuel compositions. The heat generated by flame not only depends on the flame temperature but also on the chemistry heat release of fuel and flame dimension. The study reports that the syngas/producer gas with a low H2:CO maximises the heat generation, nevertheless the higher emission rate of CO2 is inevitable. The generated heat flux at H2:CO = 3:1, 1:1, and 1:3 is found to be 222, 432 and 538 W m-2 respectively. At the same amount of heat generated, H2 concentration in fuel dominates the emission of NOx. The addition of CH4 into the syngas/producer gas with H2:CO = 1:1 also increases the heat generation significantly (e.g. 614 W m-2 at 20%) while decreases the emission formation. In contrast, adding 20% CO2 and N2 to the syngas/producer gas composition reduces the heat generation from 432 W m-2 to 364 and 290 W m-2, respectively. The role of CO2 on this aspect, which is weaker than N2, thus suggests CO2 is preferable than N2. Along with the study, the significant role of CO2 on the radiation of heat and the reduction of emission are examined.

Effect of turbulence model on flameless combustion simulation of a regenerative furnace

The high energy consumes have generated the need of developing higher efficiency devices, in this sense flameless combustion is a great alternative. The design of flameless combustion systems by means of Computational Flow Dynamics simulation is an alternative value to reduce costs, however it required an adequate model selection. In the present study a capability evaluation of standard and realizable versions of k-e turbulence model was carried out. Experimental measurements of temperature and chemical species were performed in combustion chamber of a regenerative furnace in order to compare this with numerical data and in this way determinate the performance and the incidence of the selected models. The realizable version shows better results regarding at changes of flow direction and recirculation patterns inside the furnace.

Combustion System Design of a Genset Diesel Engine by Using DFSS Methodology

In this study, an optimum design for the combustion system of a genset diesel engine was conducted by using Design for Six Sigma (DFSS) methodology. As a result of this study, the best combination of design parameters to minimize the fuel consumption of the genset diesel engine was selected while meeting the requirements of NOx emission and peak firing pressure (PFP) limit. Compared to the initial design, the final design proposal has achieved 2.5 % and 1.6 % improvement in brake specific fuel consumption (BSFC) at switchable operating conditions, i.e., both 1500 and 1800 rpm. On the basis of this DFSS work, the design robustness was also enhanced. Hence, it is expected that the final design proposal would reduce the variability in fuel economy that could be caused by harsh environment and system aging. In this study, engine cycle simulation technique was employed to assess the effects of various design parameters on the performances of the genset diesel engine. The current optimum design work has considered four control factors such as turbocharger size, air temperature at charge air cooler (CAC) outlet, compression ratio, and fuel injection duration. Here, an L9 orthogonal array was used to efficiently choose the best design proposal among 81 design combinations (i.e., four independent control factors which individually have three different levels).

Numerical investigation of two-phase reactive flow with two moving boundaries in a two-stage combustion system

The quest to achieve higher muzzle velocity is one of the key goals for researchers in the fields of propulsion and ballistic. Based on the conventional chemical propulsion, the two-stage combustion system as a new launch principle can provide higher muzzle velocity without exceeding the maximum pressure in the chamber. In this paper, the modified two-fluid model with two moving boundaries is proposed to simulate the detailed multi-dimensional flow and energy conversion behaviors of the combustion gas and propellant grains in the two-stage chamber. The dynamic self-adapting mesh update method is developed to expand and merge the computational domain for both projectile and piston motions. The application to a standard virtual gun as a standard benchmark for interior ballistic codes is used to validate the accuracy and reliability. The calculation results are in good agreement with those of codes in different countries. After that, a two-stage chamber system is set up based on the standard virtual gun. The numerical results present deep understanding of the two-phase flow behaviors in the two-stage chamber. Then the effects of design parameters on the performances in the additional chamber are numerically investigated. Finally, a suggested scheme of the additional chamber is proposed. The findings of the study put a further prediction tool for the understanding and design of the two-stage combustion system with moving boundaries.

Modeling advanced combustion modes in compression ignition engines with tabulated kinetics

New combustion modes for compression ignition engines are currently under investigation to achieve a further reduction noxious emissions and fuel consumption. Among them, partially premixed (PPC or PCCI) and dual fuel combustion (including RCCI) seem to be the most promising technologies. To support the design of new combustion systems, rapid and accurate models are required to correctly describe the fuel auto-ignition chemistry together with the complex structure of the diffusion flame due to the presence of different fuel jets. A combustion model based on tabulated kinetics was developed and presented in this work. Reaction rates and chemical composition are stored in a lookup table which is generated by processing results of auto-ignition calculations in a homogeneous reactor. Multi-component fuels are supported and the use of virtual species allows an easy integration with the Lagrangian spray model. Compared to approaches where chemical direct integration is employed, tabulated kinetics offers reduced computational time with a very similar level of accuracy such that it is suitable to be applied for engine design. The proposed approach was implemented in the Lib-ICE code which based on the OpenFOAM® technology. Validation was carried out considering conventional Diesel, PCCI and dual-fuel combustion. Satisfactory results were achieved, the proposed approach correctly predicted in-cylinder pressure development and pollutant formation in a wide range of operating conditions. The results also show that the model is consistent with energy conservation and can be applied in design phases of different engine configurations.

Combustion regimes in sequential combustors: Flame propagation and autoignition at elevated temperature and pressure

This numerical study investigates the combustion modes in the second stage of a sequential combustor at atmospheric and high pressure. The sequential burner (SB) features a mixing section with fuel injection into a hot vitiated crossflow. Depending on the dominant combustion mode, a recirculation zone assists flame anchoring in the combustion chamber. The flame is located sufficiently downstream of the injector resulting in partially-premixed conditions. First, combustion regime maps are obtained from 0-D and 1-D simulations showing the co-existence of three combustion modes: autoignition, flame propagation and flame propagation assisted by autoignition. These regime maps can be used to understand the combustion modes at play in turbulent sequential combustors, as shown with 3-D large eddy simulations (LES) with semi-detailed chemistry. In addition to the simulation of steady-state combustion at three different operating conditions, transient simulations are performed: (i) ignition of the combustor with autoignition as the dominant mode, (ii) ignition that is initiated by autoignition and that is followed by a transition to a propagation stabilized flame, and (iii) a transient change of the inlet temperature (decrease by 150 K) resulting into a change of the combustion regime. These results show the importance of the recirculation zone for the ignition and the anchoring of a propagating type flame. On the contrary, the autoignition flame stabilizes due to continuous self-ignition of the mixture and the recirculation zone does not play an important role for the flame anchoring. These findings are important for the design and operation of practical sequential combustion systems.

Key Fuel Injection System Features for Efficiency Improvement in Future Diesel Passenger Cars

<div class="section abstract"><div class="htmlview paragraph">Diesel will continue to be an indispensable energy carrier for the car fleet CO<sub>2</sub> emission targets in the short-term. This is particularly relevant for heavy-duty vehicles as for mid-size cars and SUVs. Looking at the latest technology achievements on the after-treatment systems, it can be stated that the concerning about the NOx emission gap between homologation test and real road use is basically solved, while the future challenge for diesel survival is to keep its competitiveness in the CO<sub>2</sub> vs cost equation in comparison to other propulsion systems.</div><div class="htmlview paragraph">The development of the combustion system design still represents an important leverage for further efficiency and emissions improvements while keeping the current excellent performance in terms of power density and low-end torque.</div><div class="htmlview paragraph">The paper describes the results achieved in developing a new diesel combustion system for car application that, leveraging on the high flexibility of the latest fuel injection technology, combines outstanding power and fuel efficiency with low pollutant emissions in ultralight engine designed for lower maximum peak cylinder pressure. The study has been carried out on a 0.5l single-cylinder engine on which an advanced and last generation common rail system, capable of very high injection pressure, has been installed.</div><div class="htmlview paragraph">Through an extensive DoE-based test campaign in which all engine operating parameters have been carefully parametrized, the capability to achieve high power density and excellent fuel economy with low engine-out pollutant emissions has been demonstrated and discussed in the paper.</div></div>

Avoiding CO2 capture effort and cost for negative CO2 emissions using industrial waste in chemical-looping combustion/gasification of biomass

Chemical-looping combustion (CLC) is a combustion process with inherent separation of carbon dioxide (CO2), which is achieved by oxidizing the fuel with a solid oxygen carrier rather than with air. As fuel and combustion air are never mixed, no gas separation is necessary and, consequently, there is no direct cost or energy penalty for the separation of gases. The most common form of design of chemical-looping combustion systems uses circulating fluidized beds, which is an established and widely spread technology. Experiments were conducted in two different laboratory-scale CLC reactors with continuous fuel feeding and nominal fuel inputs of 300 Wth and 10 kWth, respectively. As an oxygen carrier material, ground steel converter slag from the Linz–Donawitz process was used. This material is the second largest flow in an integrated steel mill and it is available in huge quantities, for which there is currently limited demand. Steel converter slag consists mainly of oxides of calcium (Ca), magnesium (Mg), iron (Fe), silicon (Si), and manganese (Mn). In the 300 W unit, chemical-looping combustion experiments were conducted with model fuels syngas (50 vol% hydrogen (H2) in carbon monoxide (CO)) and methane (CH4) at varied reactor temperature, fuel input, and oxygen-carrier circulation. Further, the ability of the oxygen-carrier material to release oxygen to the gas phase was investigated. In the 10 kW unit, the fuels used for combustion tests were steam-exploded pellets and wood char. The purpose of these experiments was to study more realistic biomass fuels and to assess the lifetime of the slag when employed as oxygen carrier. In addition, chemical-looping gasification was investigated in the 10 kW unit using both steam-exploded pellets and regular wood pellets as fuels. In the 300 W unit, up to 99.9% of syngas conversion was achieved at 280 kg/MWth and 900 °C, while the highest conversion achieved with methane was 60% at 280 kg/MWth and 950 °C. The material’s ability to release oxygen to the gas phase, i.e., CLOU property, was developed during the initial hours with fuel operation and the activated material released 1–2 vol% of O2 into a flow of argon between 850 and 950 °C. The material’s initial low density decreased somewhat during CLC operation. In the 10 kW, CO2 yields of 75–82% were achieved with all three fuels tested in CLC conditions, while carbon leakage was very low in most cases, i.e., below 1%. With wood char as fuel, at a fuel input of 1.8 kWth, a CO2 yield of 92% could be achieved. The carbon fraction of C2-species was usually below 2.5% and no C3-species were detected. During chemical-looping gasification investigation a raw gas was produced that contained mostly H2. The oxygen carrier lifetime was estimated to be about 110–170 h. However, due to its high availability and potentially low cost, this type of slag could be suitable for large-scale operation. The study also includes a discussion on the potential advantages of this technology over other technologies available for Bio-Energy Carbon Capture and Storage, BECCS. Furthermore, the paper calls for the use of adequate policy instruments to foster the development of this kind of technologies, with great potential for cost reduction but presently without commercial application because of lack of incentives.

Experimental study on spray and evaporation characteristics of diesel-fueled marine engine conditions based on optical diagnostic technology

The spray and evaporation characteristics of injector used in the large marine diesel engine directly affect the combustion and emission performance of marine engine. But these characteristics are rarely studied. In this work, three kinds of optical diagnostic technologies (backlight high speed imaging technique, UV-LAS and LIF/MIE) were applied to measure the spray liquid and vapor penetrations, spreading angles, SMDs and the distribution of fuel vapor mass of an injector used in the large marine engine under different conditions. The detailed description of the experiment setups and principle of the three optical diagnostic techniques are provided in this work. The experimental results show that the liquid and vapor penetrations decrease with increasing the ambient density. Increasing the ambient temperature can reduce the liquid penetration, but has no obvious effect on the vapor penetration. For spreading angle, the ambient temperature and ambient density are the main influence factors. Increasing the injection pressure is an effective method to reduce SMD, and also the ambient temperature acts as an important role in the fuel evaporation process. What’s more, the empirical correlations of spray tip penetrations and SMDs have been updated to fit the spray characteristics of marine diesel engine injector. In general, this work is helpful to understand the spray and evaporation characteristics within diesel-fueled marine engine conditions, and can provide valuable direction for the design of marine engine combustion system.

Review on modelling approaches based on computational fluid dynamics for biomass combustion systems

Biomass combustion is an important pathway of energy generation from renewable resources. Even though biomass combustion is an established conversion process, there is a high potential for further optimization of the used technologies. In particular, the advantage of numerical methods for the improvement of biomass combustion systems is not used to its full extent, because the simulation of these complex systems requires various sub-models for the thermo-chemical conversion of the biomass and sufficient computational resources for the combustion simulation. However, simulations are a valuable tool to enhance the design and operating conditions of biomass combustion systems with regard to high efficiency, low emissions and high flexibility. In addition, comparison of experimental and numerical results leads to a better understanding of the processes involved in biomass combustion. The present study gives a comprehensive overview of simulations of biomass combustion systems based on computational fluid dynamics that are available in the literature. It focusses on systems with fixed bed and covers various technologies (moving bed, pellet boilers, wood log stoves) as well as a wide range of sizes from laboratory reactors to industry scale. Besides woody biomass, also alternative fuels such as straw or municipal solid waste are considered. All relevant sub-models for the thermo-chemical conversion of the fuel on the one hand and for the gas-phase combustion on the other hand are discussed in detail. The recent advances in the concerned research fields are described.

Comparison of two measurement strategies to obtain the residence time distribution in combustion chambers using tunable diode laser absorption spectroscopy.

The residence time distribution (RTD) of fluid elements in combustion chambers is a key feature of the flow field, and its knowledge is therefore important for the design and improvement of combustion systems. The hostile yet sensitive environment of burners, in particular with high particle loads of solid-fuel firing, impede direct access to this quantity. Two strategies to obtain the RTD based on hydrogen chloride injection with subsequent detection by tunable diode laser absorption spectroscopy are directly compared and applied to gas and solid-fuel combustion under two different combustion modes. Through the direct comparison of this work, the experimentally more challenging and thus rarely utilized pulse injection was found to be superior to the commonly used step injection.

Ambient Tracer-LIF for 2-D quantitative measurement of fuel concentration in gas jets

A novel ambient tracer LIF technique with addition of tracer into ambient gas is proposed in this study to quantitatively measure the two dimensional (2-D) fuel concentration distribution in high-pressure gas jets. Firstly, the fundamental principle of the ambient tracer-LIF technique is described, and the equation of fuel concentration in a jet is deduced from the ambient fluorescence intensity. In the ambient tracer-LIF technique, the on-site calibration can be performed, and much more degrees of freedom in selection of tracers or target fuels can be achieved in principle. Then, the experiments are carried out with the high pressure gas injected into the environment doped with acetone in an optical accessible constant volume vessel. The fluorescence in the ambient is induced by using the 266 nm laser, and is recorded by the ICCD camera. The dedicated image processing is implemented to reduce the uncertainty and obtain the quantitative fuel concentration distribution in the jet. The uncertainties of the measurement results are evaluated, including both the systematic and random errors. The uncertainty propagation analysis shows that the measurement uncertainty increases with the local fuel concentration decreasing, and at the boundary regions of the jet, where the mixture is over lean, the relative uncertainty goes up to 26%. Finally, the temporal variations of the fuel concentration distribution in the gas jet are presented, and the effects of injection pressure are discussed. These results are believed to be valuable for development of numerical models and combustion system designs.

Emerging trends in numerical simulations of combustion systems

Numerical simulations have played a vital role in the design of modern combustion systems. Over the last two decades, the focus of research has been on the development of the large eddy simulation (LES) approach, which leveraged the vast increase in computing power to dramatically improve predictive accuracy. Even with the anticipated increase in supercomputing capabilities, the use of LES in design is limited by its high computational cost. Moreover, to aid decision making, such LES computations have to be augmented to estimate underlying uncertainties in simulation components. At the same time, other changes are happening across industries that build or use combustion devices. While efficiency and emissions reduction are still the primary design objectives, reducing cost of operation by optimizing maintenance and repair is becoming an important segment of the enterprise. This latter quest is aided by the digitization of combustors, which allows collection and storage of operational data from a host of sensors over a fleet of devices. Moreover, several levels of computing including low-power hardware present on board the combustion systems are becoming available. Such large data sets create unique opportunities for design and maintenance if appropriate numerical tools are made available. As LES revolutionized computing-guided design by leveraging supercomputing, a new generation of numerical approaches is needed to utilize this vast amount of data and the varied nature of computing hardware. In this article, a review of emerging computational approaches for this heterogeneous data-driven environment is provided. A case is made that new but unconventional opportunities for physics-based combustion modeling exist in this realm.

The wall-flow-guided and interferential interactions of the lateral swirl combustion system for improving the fuel/air mixing and combustion performance in DI diesel engines

The lateral swirl combustion system was designed based on and to improve upon the traditional ω-type combustion system. Previous research has verified the outstanding combustion performance of the lateral swirl combustion system. In this study, to reveal the interaction mechanisms between the lateral swirl combustion chamber and spray jets, experimental and numerical study was conducted at various spray incident angles (φ) where the relations between the combustion chamber and spray jets are different. The spray impinging processes and combustion performance were measured in a single-cylinder diesel engine with an endoscopic system. The distribution of velocity and the equivalence ratio was analyzed through simulation. Then, under the optimal φ, the fuel/air mixing quality and combustion performance was verified in comparison with a double swirl combustion system.The results show that fuel consumption and soot emissions of the lateral swirl combustion system decreased with an increasing spray incident angle. When φ reached its maximum, the combustion system exerted the best combustion performance, because the wall-flow-guided interaction between the chamber and spray jets and the interferential interaction from the neighboring wall jets were optimized. This combined effect promoted in-cylinder fuel/air mixing and combustion. Under this circumstance, the indicated thermal efficiency of the lateral swirl combustion system increased by 3.4–6.8% compared with the double swirl combustion system, and the soot emissions decreased in the ranges of 45–73%. It was concluded that the lateral swirl combustion system with a maximum spray incident angle significantly improves the combustion performance of DI diesel engines due to the wall-flow-guided and interferential interactions between the combustion chamber and spray jets. These findings are key to the design and development of a high-efficiency lateral swirl combustion system for DI diesel engines.

Dynamic Data-Driven Combustor Design for Mitigation of Thermoacoustic Instabilities

A critical issue in design and operation of combustors in gas turbine engines is mitigation of thermoacoustic instabilities, because such instabilities may cause severe damage to the mechanical structure of the combustor. Hence, it is important to quantitatively assimilate the knowledge of the system conditions that would potentially lead to these instabilities. This technical brief proposes a dynamic data-driven technique for design of combustion systems by taking stability of pressure oscillations into consideration. Given appropriate experimental data at selected operating conditions, the proposed design methodology determines a mapping from a set of operating conditions to a set of quantified stability conditions for pressure oscillations. This mapping is then used as an extrapolation tool for predicting the system stability for other conditions for which experiments have not been conducted. Salient properties of the proposed design methodology are: (1) It is dynamic in the sense that no fixed model structure needs to be assumed, and a suboptimal model (under specified user-selected constraints) is identified for each operating condition. An information-theoretic measure is then used for performance comparison among different models of varying structures and/or parameters and (2) It quantifies a (statistical) confidence level in the estimate of system stability for an unobserved operating condition by using a Bayesian nonparametric technique. The proposed design methodology has been validated with experimental data of pressure time-series, acquired from a laboratory-scale lean-premixed swirl-stabilized combustor.

Impact of hydrocracked diesel fuel and Hydrotreated Vegetable Oil blends on the fuel consumption of automotive diesel engines

The present paper describes the results of a research activity aimed to assess the potential of hydrocracked fossil oil (HCK) and Hydrotreated Vegetable Oil (HVO) blends, as future premium diesel fuels, on fuel consumption (FC) reduction of the modern automotive diesel engines.Three fuels have been formulated and tested in a light duty four-cylinder diesel engine, Euro 5 version, equipped with closed loop control of the combustion. The set of fuels comprised three experimental fuels formulated ad hoc by blending HVO and HCK streams, and an EN590-compliant commercial diesel fuel representative of the current market fuel quality.A specific test procedure based on a sequence of New European Driving Cycle (NEDC) and ARTEMIS cycles on an engine dyno test bed was applied in order to carry out accurate fuel consumption measurements versus fuel quality, so reproducing the fuel effects on FC for long mileage use of the vehicle.Results of the experimental activity proved that HCK-HVO blends give a benefit on both FC and CO2 saving. Taking into account the strong similarity in terms of combustion system design between Euro 5 and Euro 6 engines, the estimated trends can be considered valid also for Euro 6 vehicles equipped with the same class of engines. In a next step, it is planned to validate these results by carrying out also WLTP and RDE emission tests.

Approximation of laminar flame characteristics on premixed ammonia/hydrogen/nitrogen/air mixtures at elevated temperatures and pressures

Ammonia shows a promising potential to be a carbon-free and sustainable fuel for gas turbines and internal combustion engines. The design of such complex combustion systems using computational reactive fluid dynamics in combination with detailed reaction mechanisms is a time-consuming challenge. Combustion models are a solution to reduce the computation time, but require data of fundamental laminar flame characteristics. In order to provide such data, in this present study correlations of laminar flame speed and flame thickness for ammonia/hydrogen/nitrogen/air mixtures based on a prior selected detailed reaction mechanism were developed. A validation study for three detailed chemical schemes was conducted using experimentally obtained laminar flame speed data from literature to determine one mechanism with the best predictive capabilities. A database with 222250 data entries of laminar flame speed and flame thickness was generated by performing numerical one-dimensional simulations using the selected mechanism. From that correlations were derived. The database as well as the derived correlations contain a broad range of initial conditions: air/fuel equivalence ratio: (0.5–1.7), ammonia: (0–100) mol%, hydrogen addition: (0–60) mol%, nitrogen addition: (0–20) mol%, fresh gas temperatures: (300–1100) K and pressures: (0.1–25) MPa. For the substitution of fuel within existing burners or engines which so far are operated with methane, it is of special interest, if a defined ammonia/hydrogen/nitrogen/air mixture could be used with similar properties. For that it is shown that such a mixture composition can be found which has a similar laminar flame speed than methane, depending on the given initial conditions.