Potential for Carbon-Neutral Advanced Biofuels in UK Road Transport

As a result of anthropocentric climate change, there is an urgent need to decarbonize the supply of energy. Organic biomass, referred to as feedstock, can be converted into biofuels that have the potential to decarbonize transport. However, biofuels are typically not carbon neutral because the preparation of feedstocks and the production of biofuels require energy currently supplied by fossil fuels, which involve carbon emissions. This work aimed to bring biofuel research up to date with current UK policy of net zero carbon emissions by examining the volume of carbon-neutral advanced biofuels that could be produced from sustainable feedstocks generated in the UK. By analyzing relevant data, it is estimated that between 667 and 1,791 million litres (Mltr) of carbon-neutral biodiesel equivalent could be produced with the energy content of 22.7–60.9 PJ, corresponding to 8.1%–21.7% of current diesel consumption by heavy goods vehicles in the UK

Dynamics Analysis of a Jet-Fuel Surrogate and Development of a Skeletal Mechanism for Computational Fluid Dynamic Applications

The autoignition dynamics of a three-component surrogate jet fuel (66.2% n-dodecane, 15.8% n-proplylbenzene, 18.0% 1,3,5-trimethylcyclohexane) suitable for usage as Jet A-1 and RP-3 aviation fuels are analyzed, using the detailed mechanism of Liu et al. (2019). The conditions considered are relevant to the operation of gas turbines and the analysis is performed using mathematical tools of the computational singular perturbation (CSP) method. The key chemical pathways and species are identified in the analysis of a homogeneous adiabatic and constant pressure ignition system for a wide range of initial conditions. In particular, the key role of hydrogen and CO-related chemistry is highlighted, with an increasing importance as the initial temperature increases. The C2H4→C2H3→CH2CHO pathway is also identified as playing a secondary but nonnegligible role with an importance increasing with initial temperature, favoring the system’s explosive dynamics and, thus, promoting ignition. Finally, C2H4 is identified as being a species with a key (secondary) role to the system’s explosive dynamics, but its role is replaced by C3H6 and, eventually, by O2 as the initial temperature increases. In the second part of the current work, a 58-species skeletal mechanism is generated using a previously developed algorithmic process based on CSP. The developed skeletal mechanism was tested in a wide range of initial conditions, including both ignition delay time and laminar flame speed calculations. For the conditions that were of interest in the current work, the skeletal mechanism approximated the detailed mechanism with very small error. The 58-species skeletal mechanism is shown to be ideal for use in computational fluid dynamics applications not only because of its small size but also because of its sufficiently slow associated fast timescale

Computational investigation of ammonia-hydrogen peroxide blends in HCCI engine mode

The potential use of hydrogen peroxide as an ignition promoter to enable the use of ammonia in compression ignition engines is explored in the current study. A simplified numerical HCCI engine model within the Chemkin Pro suite is employed. The numerical investigation reveals that the proposed use of hydrogen peroxide is significantly more advantageous against the more conventional method of preheating the intake charge to achieve ignition, whilst using a glow plug. In particular, the IMEP, power and torque exhibit an increase greater than 65% along with a spectacular decrease of NOx emissions reaching in certain cases a 9-fold decrease. The thermal efficiency exhibits a more moderate, yet non-negligible increase, around 5%. Generally, the incremental increase of hydrogen peroxide leads to the increase of the IMEP, power and torque as well as the maximum temperature and, hence, NOx emissions. These increases are largely linear with the hydrogen peroxide addition. Finally, the introduction of hydrogen peroxide leads to a two-stage ignition process, where the first ignition stage was found to be instrumental to the control of the ignition process, and, therefore, the system’s efficiency. Further research is required to substantiate further the feasibility and the the limitations of the proposed technology which can enable the rapid decarbonization of heavy duty applications, such as marine ships and trucks

Dynamics Analysis of a Jet-Fuel Surrogate and Development of a Skeletal Mechanism for Computational Fluid Dynamic Applications

The autoignition dynamics of a three-component surrogate jet fuel (66.2% n-dodecane, 15.8% n-proplylbenzene, 18.0% 1,3,5-trimethylcyclohexane) suitable for usage as Jet A-1 and RP-3 aviation fuels are analyzed, using the detailed mechanism of Liu et al. (2019). The conditions considered are relevant to the operation of gas turbines and the analysis is performed using mathematical tools of the computational singular perturbation (CSP) method. The key chemical pathways and species are identified in the analysis of a homogeneous adiabatic and constant pressure ignition system for a wide range of initial conditions. In particular, the key role of hydrogen and CO-related chemistry is highlighted, with an increasing importance as the initial temperature increases. The C2H4→C2H3→CH2CHO pathway is also identified as playing a secondary but nonnegligible role with an importance increasing with initial temperature, favoring the system’s explosive dynamics and, thus, promoting ignition. Finally, C2H4 is identified as being a species with a key (secondary) role to the system’s explosive dynamics, but its role is replaced by C3H6 and, eventually, by O2 as the initial temperature increases. In the second part of the current work, a 58-species skeletal mechanism is generated using a previously developed algorithmic process based on CSP. The developed skeletal mechanism was tested in a wide range of initial conditions, including both ignition delay time and laminar flame speed calculations. For the conditions that were of interest in the current work, the skeletal mechanism approximated the detailed mechanism with very small error. The 58-species skeletal mechanism is shown to be ideal for use in computational fluid dynamics applications not only because of its small size but also because of its sufficiently slow associated fast timescale

Modelling the Transmission of Coxiella burnetii within a UK Dairy Herd: Investigating the Interconnected Relationship between the Parturition Cycle and Environment Contamination

Q fever infection in dairy herds is introduced through the transmission of the bacterium Coxiella burnetii, resulting in multiple detrimental effects such as reduction of lactation, abortions and chronic infection. Particularly in the UK, recent evidence suggests that the infection is endemic in dairy cattle. In this work, we investigate the dynamics of the disease with the aim to disentangle the relationship between the heterogeneity in the shedding routes and their effect on the environmental contamination. We develop a mathematical model for the transmission of Q fever within UK cattle herds by coupling the within-herd infection cycle of the disease with farm demographics and environmental effects, introduced by either the indoor or outdoor environment. Special focus is given on the mechanism of transmission in nulliparous heifers and multiparous cattle. We calibrate the model based on available knowledge on various epidemiological aspects of the disease and on data regarding farm demographics available in the UK DEFRA. The resulting model is able to reproduce the reported prevalence levels by field and in silico studies, as well as their evolution in time. In addition, it is built in an manner that allows the investigation of different housing techniques, farm management styles and a variety of interventions. Sensitivity analysis further reveals the parameters having the major effect in maintaining high prevalence levels of seropositive and shedding cattle. The present analysis aims also to indicate the gaps in the available data required to optimise the proposed model or future models that will developed on the basis of the one proposed herein. Finally, the developed model can serve as mathematical proof for the assessment of various interventions for controlling the dynamics of Q fever infection

Engine performance and emissions from a fumigated hydrogen/ammonia compression ignition engine with a hydrogen peroxide pilot

The study investigates, numerically, the potential use of introducing aqueous HO as an ignition promoter in a statistically homogeneous NH/H fuelled, medium speed (1250 rpm), 4-stroke, 1.3 litre cylinder displacement, mildly boosted CI engine with a compression ratio of 17.6:1. The H is considered to be produced on-board from ammonia cracking. An extensive campaign is undertaken using the commercial stochastic reactor model, SRM Engine Suite, which allowed the modelling of temporal, temperature and spatial stratification in the cylinder. The engine performance, combustion phasing, maximum pressure rise rate and emissions (NOx, NO and unreacted NH) are investigated in view of: (i) the share of molecular hydrogen in the initial NH/H mixture from 10 to 40 percent; (ii) the mass of aqueous HO introduced from 0.1 to 16 mg; (iii) the start of injection (−10 to ＋6 CAD aTDC) and duration of injection (1, 4 and 8 CAD); (iv) the amount of exhaust gas recirculation (up to 30 percent by mass); (v) the share of energy from the HO in the aqueous solution mixture at less than 0.5 percent of that in the main fuel; (vi) engine load corresponding to a variation in the equivalence ratio from 0.32 to 1.2 by changing the mass of the NH/H mixture in the combustion chamber. A wide range of loads (evaluated against the engine’s rated power when operated with diesel and at its rated boost levels) can be achieved (44%–93%) with the energy share of HO being as little as equivalent to 2.7% vol% that of the main fuel, ammonia, which is introduced into the cylinder. This implies that the required storage volume of the HO is low, at a few percent that of the main ammonia tank. NOx emissions peak between .6−0.65 and rapidly decrease as the equivalence ratio increases or decreases reaching values marginally above the Tier III standard at high loads (90%) while ammonia slip and NO emissions are generally extremely low (10−12 mg for NH and 0.01 mg/kWh for NO)

Computational singular perturbation analysis of brain lactate metabolism

Lactate in the brain is considered an important fuel and signalling molecule for neuronal activity, especially during neuronal activation. Whether lactate is shuttled from astrocytes to neurons or from neurons to astrocytes leads to the contradictory Astrocyte to Neuron Lactate Shuttle (ANLS) or Neuron to Astrocyte Lactate Shuttle (NALS) hypotheses, both of which are supported by extensive, but indirect, experimental evidence. This work explores the conditions favouring development of ANLS or NALS phenomenon on the basis of a model that can simulate both by employing the two parameter sets proposed by Simpson et al. (J Cereb. Blood Flow Metab., 27:1766, 2007) and Mangia et al. (J of Neurochemistry, 109:55, 2009). As most mathematical models governing brain metabolism processes, this model is multi-scale in character due to the wide range of time scales characterizing its dynamics. Therefore, we utilize the Computational Singular Perturbation (CSP) algorithm, which has been used extensively in multi-scale systems of reactive flows and biological systems, to identify components of the system that (i) generate the characteristic time scale and the fast/slow dynamics, (ii) participate to the expressions that approximate the surfaces of equilibria that develop in phase space and (iii) control the evolution of the process within the established surfaces of equilibria. It is shown that a decisive factor on whether the ANLS or NALS configuration will develop during neuronal activation is whether the lactate transport between astrocytes and interstitium contributes to the fast dynamics or not. When it does, lactate is mainly generated in astrocytes and the ANLS hypothesis is realised, while when it doesn’t, lactate is mainly generated in neurons and the NALS hypothesis is realised. This scenario was tested in exercise conditions

Asymptotic analysis of detonation development at SI engine conditions using computational singular perturbation

The occurrence and intensity of the detonation phenomenon at spark-ignition (SI) engine conditions is investigated, with the objective to successfully predict super-knock and to elucidate the effect of kinetics and transport at the ignition front. The computational singular perturbation (CSP) framework is employed in order to investigate the chemical and transport mechanisms of deflagration and detonation cases in the context of 2D high-fidelity numerical simulations. The analysis revealed that the detonation development is characterised by: (i) stronger explosive dynamics and (ii) enhanced role of convection. The role of chemistry was also found to be pivotal to the detonation development which explained the stronger explosive character of the system, the latter being an indication of the system's reactivity. The role of convection was found to be enhanced at the edge of the detonating front. Moreover, the increased contribution of convection was found to be related mainly to heat convection. Remarkably, the detonation front was mainly characterised by dissipative and not explosive dynamics. Finally, diffusion was found to have negligible role to both examined cases

Computational analysis of the effect of hydrogen peroxide addition on premixed laminar hydrogen/air flames

In the current work, the effect of H2O2 addition on the flame structure, laminar flame speed and NOx emissions is investigated in the context of 1D laminar premixed H2/air flames at Tu = 300 and 600 K, p = 1 and 30 atm, = 0.5. Mathematical tools from the computational singular perturbation approach are used in order to identify the key chemical and transport mechanisms. The H2O2 addition causes a significant increase to the laminar flame speed (sL), heat release (Q) and NOx emissions. Indicatively, 10% H2O2 addition (per fuel volume) at Tu = 300 K, p = 1 atm results in 72% increase of sL, 100% increase of Q, and 140% increase of the mass fraction of NO. Depending the conditions the flame structure is altered through the chain carrying reaction 10f (H2O2 + H H2O + OH) or the chain branching 9f (H2O2 (+M) 2OH (+M)); the first is favored at low temperatures/pressures while the latter is favored at sufficiently high temperatures/pressures. Both reactions boost the radical pool generation, therefore contributing to the broadening of the reaction zone. The reaction with the largest contribution to Q that is mostly affected (decreased) by the addition of H2O2 is reaction 21 (H + O2 (+M) HO2 (+M)). Moreover, the H2O2 addition enhances the stability of the flame. Finally, the increased production of NO is mainly associated with the increased temperature that is reached with the addition of H2O2

The chemical dynamics of hydrogen/hydrogen peroxide blends diluted with steam at compression ignition relevant conditions

In the current work, the use of hydrogen peroxide as an additive to hydrogen/air mixtures is proposed and explored computationally, in conditions relevant to compression ignition engines. The hydrogen/hydrogen peroxide blends are supplemented with steam for NOx emissions reduction purposes.The objective of the current work is to explore fundamental aspects of the proposed technology, with an emphasis on identifying the key chemical pathways that control the ignition delay time and NOx emissions, using mathematical tools from the computational singular perturbation (CSP) approach.The proposed technology demonstrates a noteworthy potential for use in CI engines, since a 10% (per fuel volume) addition of hydrogen peroxide decreases the ignition delay time to 1 ms, while the mass fraction of NO in equilibrium drops by 100%. Reactions H + O2 → OH + O and H + O2 (+M) → HO2 (+M) play key roles in the acceleration of the ignition delay time, while the thermal and the NNH mechanisms are identified as the dominant pathways for the production of NO. A further 12% addition of steam (per mixture’s volume) induces a two orders of magnitude drop to NO emissions and slightly increases the ignition delay time by 8%. Finally, at sufficiently high steam addition conditions (in the region of 30% and above by mixture’s volume), the system exhibits two stage ignition (mainly owed to reaction HO2 + OH → H2O + O2), a phenomenon that is unique, considering that the initial mixture includes solely hydrogen-based chemical species