Ignition Combustion Research Articles

On the metals compatibility assessment for oxygen service

This review article critically analyzes the selection and compatibility assessment framework of metallic alloys in pure oxygen (>99.5%) atmospheres using promoted combustion and particle impact ignition tests in combination with the Pressure-Velocity (PV) curves. The historical test data for four important metallic alloys frequently used in the oil and gas industry, namely nickel alloys C276 and 600, stainless steel 304 and 316, are mined and analyzed to: (i) capture trends and correlation of data obtained by these two tests with the PV curves, (ii) identify gaps in the data for critical process variables such as temperature, pressure and gas velocity, (iii) identify limitations of the two tests, (iv) understand the relevance of shape factors and geometry of test samples and flowing vs. non-flowing conditions on test results and (v) evaluate whether exemption pressures and PV curves can be extended or adjusted for important metals to accommodate more demanding conditions. In industry practices, PV curves are utilized to impose velocity limitations in oxygen systems to help mitigate particle impact ignition when the operating pressures are greater than alloys exemption pressures. Our analysis shows, current version of PV curves - based primarily on historical data and industry experience are conservative, limited to specific thicknesses and available only up to 200 °C for both exempt and non-exempt alloys. For the oil and gas industry where conditions up to 300°C and 80 bar are desired, there is a need to conduct new testing to develop guidelines for thinner cross-sections and more demanding operating conditions including higher temperatures and pressures.This will open avenues for new innovations and applications of gaseous oxygen and help industries operate their plants with higher efficiencies.

Effect of Polymeric Additives on Ignition, Combustion and Flame Characteristics and Soot Deposits of Crude Oil Droplets

ABSTRACT Many oil fires have resulted from the crude oil train derailments in recent years. Given the importance of crude oil shipping by rail to the energy security of the US, it is important to consider various methods that will decrease the likelihood of crude oil catching fire in case of a crude oil derailment. Present study examines the effect of polybutadiene polymer on the combustion properties and soot deposits of Bakken crude. Treating crude oil as multicomponent liquid fuels and polybutadiene as an additive, droplet combustion experiments were conducted with sub-millimeter sized spherical droplets suspended on very fine support fibers. Polybutadiene polymer additive of two different chain lengths has been investigated. Results show that both polymer chain length and origin of crude oil have a significant effect on various combustion properties like combustion rate, ignition delay, and total combustion time. Polymeric additives also change the soot deposit structure and particle size compared to the base fuel. Present research is envisioned to aid in understanding combustion behavior of crude oil as isolated droplets, as well as to generate interest in investigating more polymeric additives for liquid fuels.

Direct ink writing of nAl/pCuO/HPMC with outstanding combustion performance and ignition performance

Direct ink writing promotes ink formulation design gradually become a hotspot in the application research of nanothermite. In order to obtain an energetic ink with a certain mechanical strength and formability, it is necessary to compound the energetic material with an inert binder. The inert component will not only reduce the sensitivity and energy release efficiency of energetic systems, but also affect its application in micro ignition devices. Based on the thermal gelation behavior of hydroxypropyl methylcellulose (HPMC), the nAl/pCuO/HPMC ink was prepared by HPMC, nano aluminum powder (nAl), and sheet-like porous CuO (pCuO). It has found out that the energetic ink has a favorable printing accuracy when the HPMC content is 7 wt%. To compare the influence from the size and morphology of copper oxide and aluminum on ink printing and reaction performances, the mAl/pCuO/HPMC, nAl/nCuO/HPMC and nAl/mCuO/HPMC inks have been prepared using the same way. Due to the large particle size of the components, nAl/mCuO/HPMC cannot be printed continuously during the printing process. For the mAl/pCuO/HPMC, it cannot form self-sustaining combustion on the glass substrate when the ink is a single layer. The activation energy results show that nAl/pCuO/HPMC has the smallest value (68.39 kJ/mol). The calculated burning rate of nAl/pCuO/HPMC (32.56 cm/s) is about 6 times than that of nAl/nCuO/HPMC system (5.28 cm/s). The ignition performance test shows that only the nAl/pCuO/HPMC system can be successfully ignited by a SCB micro igniter when the HPMC content is 7 wt%. Meanwhile, the pressure test indicates that the nAl/pCuO/HPMC system (7 wt% HPMC, Ф=1.4) has the shortest pressure rising time (46.7 μs), but the largest pressurization rate (1661.7 GPa/s).

Influence of Combustion Chamber Shapes and Nozzle Geometry on Performance, Emission, and Combustion Characteristics of CRDI Engine Powered with Biodiesel Blends

Environmentally friendly, renewable, and green fuels have many benefits over fossil fuels, particularly regarding energy efficiency, in addition to addressing environmental and socioeconomic problems. As a result, green fuels can be used in transportation and power generating applications. Furthermore, being green can ably address the emission-related issues of global warming. In view of the advantages of renewable fuels, two B20 fuel blends obtained from methyl esters of cashew nutshell (CHNOB), jackfruit seed (JACKFSNOB), and jamun seed oils (JAMSOB) were selected to evaluate the performance of a common rail direct injection (CRDI) engine. Compatibility of the nozzle geometry (NG) and combustion chamber shape (CCS) were optimized for increased engine performance. The optimized CCS matched with an increased number of injector nozzle holes in NG showed reasonably improved brake thermal efficiency (BTE), reduced emissions of smoke, HC, and CO, respectively, while NOx increased. Further combustion parameters, such as ignition delay (ID) and combustion duration (CD) reduced, while peak pressure (PP) and heat release rates (HRR) increased at the optimized injection parameters. The CRDI engine powered with JAMSOB B20 showed an increase in BTE of 4–5%, while a significant reduction in HC and CO emissions was obtained compared to JACKFSNOB B20 and CHNOB B20, with increased NOx.

Investigating Combustion Process of N-Butanol-Diesel Blends in a Diesel Engine with Variable Compression Ratio

The search for alternative fuels for internal combustion engines is ongoing. Among the alternatives, plant-based fuels can also be mentioned. Alcohol is not a common fuel for diesel engines because the physical and chemical properties of the alcohols are closer to those of gasoline. In our research, the combustion properties of diesel-n-butanol mixtures have been investigated to obtain results on the effect of butanol blending on combustion. Among the combustion properties, ignition delay, in-cylinder pressure, and heat release rate can be mentioned. They have been observed under different compression conditions on an engine on which the compression ratio can be adjusted. The method used was a quite simple one, so the speed of the engine was set to a constant 900 rpm without load, while three compression ratios (19.92, 15.27, and 12.53) were adjusted with a fuel flow rate of 13 mL/min and the pre-injection angle of 18° BTDC. Blending butanol into the investigated fuel does not significantly affect maximal values of indicated pressure, while much more effect on the pressure rising rate can be detected. Furthermore, heat release rate and ignition delay increased at every compression ratio investigated. Despite the low blending rates of butanol in the mixtures, butanol significantly affects the combustion parameters, especially at high compression ratios.

Egg shell catalyst and chicken waste biodiesel blends for improved performance, combustion and emission characteristics

Over the past few years, the research on the replacement of fossil fuel from inedible oil has been gaining more and more interest owing to the positive approach done on the waste animal fat for the reusable purpose. The performance, emission and combustion characteristics were measured for both diesel and chicken fat biodiesel blends (CFB). A small single cylinder, four stroke, air cooled, combustion ignition engine was used to conduct all tests. The biodiesel was produced by using transesterification process with the chicken eggshell dominated catalyst. The derived catalyst from the waste chicken eggshell was CaO used as a catalyst for the esterification process. The biodiesel blends used for conducting tests were B10 (10% of Chicken fat biooil + 90% diesel), B30 (30% of Chicken fat biooil + 70% diesel), B50 (50% of Chicken fat biooil + 50% diesel) and D100 or B0 (100% diesel). The Brake power (BP), Brake torque, Exhaust Gas Temperature (EGT), Brake specific fuel consumption (BSFC) and emission of CO, CO2, NOx and HC for all fuel blends were calculated and compared with pure diesel B0. All tests were conducted at different engine speed as 1800 rpm, 2000 rpm, 2200 rpm, 2400 rpm and 2600 rpm. From the performance qualities results, the biodiesel blends increased the brake power, BTE, EGT and HRR while reduced the CO, HC and smoke emissions. However, there was a little increment in NOX emission. The CFB is helpful in both overcoming the shortage of fossil fuel and better waste management.

Non-equilibrium plasma for ignition and combustion enhancement

This review is intended to give an overview of recent results on plasma-assisted ignition and combustion. The influence of electrical discharges on combustion processes is introduced, and the excited species and radicals present in large quantity in the plasma are detailed. A description of theoretical problems related to modeling plasma-assisted combustion is given, elucidating the role of excited states in enhancing the reaction rates. Then some experiments are reported, focused on fundamental aspects on the effects of high pressure discharges in improving the ignition of combustion. To conclude, some applications for plasma-assisted combustion and detonation are presented, activated by different kinds of discharges.

Study on the combustion behavior and soot formation of single coal particle using hyperspectral imaging technique

This paper proposes a hyperspectral imaging technique for capturing radiative images at a high temporal–spatial resolution, for the purpose of spectrally visualizing the instantaneous combustion behaviors of single coal particles. We initially use a hyperspectral imaging device to record the combustion processes of two types of single pulverized coal particles on a McKenna flat-flame burner. From the snapshot images captured by the device, we observe the combustion processes, ignition characteristics, flame morphologies, and sizes of the two single coal particles. The observations indicate that the two single coal particles undergo volatile release/combustion and char ignition/oxidation during the luminous combustion process; moreover, both particles exhibit homogeneous ignition characteristics under the experimental conditions. Furthermore, based on the spectral radiative intensity images obtained via the device, the soot temperature and volume fraction images of the two single coal particles in the envelope flame are obtained at different burning times. Thereafter, the influences of the combustion behaviors and soot formation mechanisms on the distribution rules of the soot temperature and concentration at different combustion periods are discussed. Finally, the temperature and apparent spectral emissivity values of the two single char particles during the char oxidation process are also calculated to analyze their combustion behaviors. The results show that the temperature changes within a relatively narrow range with respect to the burning time during the oxidation stage, whereas the spectral emissivity continues to increase with the oxidation of chars and subsequently decreases.

Energy characterization of an innovative non-equilibrium plasma ignition system based on the dielectric barrier discharge via pressure-rise calorimetry

A dielectric barrier discharge igniter (BDI) ensures engine stable combustion at lean and/or diluted conditions by the generation of non-equilibrium low-temperature plasma (LTP), strong promoter of the ignition, in a wide mixture volume.Beside this, a substantial amount of thermal energy is also released in the medium to enhance the chemical reactions of fuel oxidation. Therefore, the measurement of thermal energy is crucial to characterize the igniter capability to guarantee a robust combustion onset and it can be performed only in controlled environments.In this work, a Radio-Frequency BDI was tested via pressure-based calorimetry by evaluating the thermal energy released during the discharge in a controlled environment represented by a constant volume vessel. The corresponding thermal efficiency was evaluated as well. Pure nitrogen and air were exploited at engine-relevant pressure levels by varying the discharge features as its time duration and intensity (the latter by peak electrode voltage variation), to fully characterize the igniter behavior.Both media showed similar trends of absorbed and released energy but differences up to 50% were found for the latter. This trend was found to be linear, unexpectedly in contrast to the quadratic one showed by the LTP corona streamer-type igniter (CSI). Furthermore, the thermal energy dependence from pressure showed a change up to complete independence at a specific electrode value. To provide an explanation for such different behaviors, a comparative analysis between the diverse discharges of the two igniters was carried out. Moreover, by varying voltage and duration, the device was found to be able to release up to 60 mJ in the tested point with very low dispersion, essential to guarantee stable combustion ignition at challenging operating conditions for next-generation internal combustion engines.

A Review of Performance and Emission Characteristics of a Catalytic Coated CI Engine with Biodiesel

This paper is a review outline of references of CI engine (Combustion Ignition Engine) journals. CI Engine is the most preferred sort of engine as a result of its high thermal efficiency than any other internal or external combustion engine. Due to the demand for petroleum fuel, increasing cost, and hazardous emission by CI Engine, it is required to enhance the performance, combustion, and emission characteristics of CI Engine. Bio-fuels are well-tried to be superb substitutes for the present diesel. Nowadays, numerous researches are going on in biodiesel blends at varying ratios to increase the performance of the engine. Also many researches are going on coating the piston head in order to reduce the black smoke at the exhaust.

A CFD study of ignition of lean propane-air mixtures in a heat recirculating U-bend catalytic microreactor

Heat recirculating (HR) geometries have been studied in the literature for their use in energy generation applications. This work investigates the ignition and cold-start behavior of lean propane-air combustion in a U-bend catalytic microreactor through computational fluid dynamics (CFD) study. Although several studies have focused on stability and combustion behavior, the role of heat recirculation on catalytic and homogeneous ignition from the cold-start conditions has not been analyzed so far. The U-bend microreactor is a typical example of HR geometry, where the hot exhaust gases in the recirculation channel transfer heat to the cold incoming fluid. Significance of heat recirculation across the dividing wall on the ignition temperature, as well as transient evolution of temperature, propane conversion and reaction are presented. Ignition temperature is found to be 20K lower in the U-bend microreactor than straight channel microreactor. However, transient ignition study revealed that at nominal conditions, U-bend microreactor takes about 35s longer than straight channel for ignition and to reach steady state, owing to heat distribution internally within the U-bend microreactor. The effect of flowrate is analyzed, which shows that at higher flowrates, the ignition and steady-state times are also lower for the U-bend microreactor. Finally, the effect of solid wall material is investigated, which shows that lower conductivity material (such as ceramic) showed faster ignition with low thermal inputs.

Combustion and emission study of sandbox seed oil biodiesel performance in a compression ignition (CI) engine

Transportation is a crucial aspect of global development and the utilization of fossil fuels in most combustions systems seems inevitable. This class of fuel has led greatly to worldwide environmental pollution with its attendant effects on human health and climate changes. Biofuels from biomass are sustainable and viable alternatives that can eliminate the problems associated with petroleum fuels and are most compatible with the existing combustion systems. Biodiesel will further ensure positive energy equilibrium through the conservation of natural resources to improve economic stability, environmental safety and a balanced ecosystem. Most previous works make use of edible oils, which can lead to food security and price challenges. With the abundance of non-edible oil sources unexploited, the choice of this study is directed towards producing biodiesel from a non-edible seed with little or no information on its combustion properties. This study extracted Sandbox (Hura crepitans) oil chemically using analytical n-hexane as solvent and subsequently produced biodiesel from the oil via one step-transesterification. The biodiesel was characterized according to global standards for biodiesel (ASTM D6751 and EN 14214) and blended with petrodiesel to give five fuel samples (D100, B10, B20, B30 and B100). These fuels were combusted in a compression ignition (CI) engine test bed to determine its performance and emission characteristics. The results showed that the Sandbox seed produced oil with a good oil yield of 47.77% and the biodiesel produced had a yield of 86.49%, which satisfies the recommended global standards. B10 exhibited the best and highest BTE after D100 at all the torque levels (4 Nm, 6 Nm and 7 Nm) as well as the least and the most desirable emission of CO2 when compared with all the other fuels. The utilization of Sandbox biodiesel in combustion ignition engine was found to be a viable option at enhancing biofuel utilization and reduction of pollutant emissions from the present combustion of fossil fuels.

Analysis of PPCI mode and multi-objective comprehensive optimization for a dual-fuel engine

The aim of this research is to find a favorable combination of the complex control parameters of a diesel/natural gas dual-fuel engine, so that polluting emissions can meet regulatory requirements and achieve relatively low fuel consumption. This research covers the effects of control parameters on the performance and emissions of a dual-fuel engine for different combustion modes as well as discussions on the optimization of the entire operating conditions in the partial premixed compression combustion ignition (PPCI) mode combined with long short-term memory networks (LSTM) and non-dominated sorting genetic algorithms (NSGA-II). LSTM is used for the first time to establish a predictive regression model for the calibration parameters and output response of a dual-fuel engine, achieving the optimized mapping of input and output parameters. All of the optimization scenarios can achieve a trade-off between fuel consumption and emissions. The engine test results show that for the entire working conditions for the optimized dual-fuel engine, the nitrogen oxides (NOx) emissions are reduced by 77%, and the fuel consumption is roughly equal to that of the original diesel engine. The test results of the four condition test cycle of a marine engine for propulsion show that the NOx emissions of the optimized dual-fuel engine are reduced by 26.6% compared with the Tier-III legal requirements.

Measurement of combustion properties and ignition delay time of high performance alternative aviation fuels

High-energy density aviation fuels are tested to see feasibility as alternative fuels to conventional jet fuels. They are derivatives of the existing high-energy density hydrocarbon fuels, exo-tetrahydrodicyclopentadiene and exo-tetrahydrotricyclopentadiene. Combustion properties and ignition delay times of these alternative fuels, called high performance fuels (HPF-1 and 2) are measured. Densities of HPF-1 and HPF-2 are similar to density of exo-tetrahydrodicyclopentadiene, but their H/C ratio, molecular weight, heat of combustion, derived cetane number, and threshold sooting index are quite higher than those of exo-tetrahydrodicyclopentadiene. It is found that HPF-1 and 2 have higher heat of combustion and lower sooting propensity than conventional jet aviation fuels when they are compared at the same fuel density. On the other hand, ignition delay time is measured in a temperature range from 950 K to 1,300 K at 12 atm by using a shock tube. Results show that ignition delay time of the two fuels is shorter than exo-tetrahydrodicyclopentadiene. HPF-2 containing methylcyclohexane has much shorter ignition delay time than exo-tetrahydrodicyclopentadiene at high temperature over 1,050 K.

A comparative study on alcohol-diesel blended fuels in a common rail diesel engine: Combined effects of carbon numbers, oxygen content, and molecular structure

Abundant alcohols, including ethanol, propanol, butanol, and pentanol, are expected to be used in compression ignition engines to ease the shortages of fossil fuel. The various alcohols have quite a different combustion and emission characteristics in the engine due to the changes in molecular structures. In this paper, a series of experiments were conducted on a modified common-rail diesel engine fueled with diesel/alcohols blended fuels in a wide operating range. The effects of alcohol chain length, oxygen content, and molecular structure on engine combustion and emission characteristics are studied systematically. The experimental results show that the blending of alcohols increases the peak values of in-cylinder pressure and maximum pressure rising rate. Besides, the combustion duration and ignition delay are mainly affected by oxygen content and isomer structure. The addition of short-chain alcohols will significantly reduce the total mass of particulate matter (PM) emissions, while the CO and HC emissions increase appropriately. The CO, HC, aldehydes, and ethylene emissions are mainly affected by carbon chain length and isomer structure. For PM emissions, the carbon chain length, molecular structure, and oxygen content of alcohol fuels have different influences on PM number, PM mass, and particle size distributions. The shorter carbon chain of alcohol leads to smaller particle size, and higher oxygen content leads to lower total particle mass.

SVM, ANN, and PSF modelling approaches for prediction of iron dust minimum ignition temperature (MIT) based on the synergistic effect of dispersion pressure and concentration

Data-driven models for predicting fire and explosion-related properties have been improved greatly in recent years using machine-learning algorithms. However, choosing the best machine learning approach is still a challenging task. Therefore, in this study, the predictability comparisons have been made with the different machine learning methods used to model the MIT for iron dust. The MIT of iron dust was determined using the Godbert-Greenwald furnace for seventy unique combinations of dispersion pressures and dust concentrations. The data has been divided into 'Training Set' and 'Testing Set'. The implementation and efficacy of machine learning and statistical approaches have been demonstrated through real-time experimental results. The support vector machines (SVM) regression models were trained with various kernel functions to enhance the performance of the resultant model. The cubic kernel function was found suitable for training SVMs. Besides, a feed-forward artificial neural network with the backpropagation algorithm and a polynomial surface fit model have also been developed to predict the MIT. For statistical phenomena, such as MIT, predictive modelling based on real-time experimental data is critical. If an accurate estimate of the combustible dust's minimum ignition temperature is confirmed, it is possible to ensure that the temperatures of the surrounding hot surfaces do not rise to that level, preventing an explosion. An overall comparison of predictive models has been given with unseen test data set. All the trained models yielded comparable results with unseen test data set. However, the SVM model with Bayesian optimizer approach can effectively assess the risk of ignition based on dust MIT under the influence of dispersion pressure and dust cloud concentration among all the approaches adopted in this study.

Prediction of performance parameters of a four stroke diesel engine experimented with blends of vegetable oil biodiesel

Fossil fuel consumption is increasing in a massive amount due to its applications in various sectors. Moreover, use of such fuels creating harmful fumes and gases, which in turn creating an impact on the environment. To reduce the impact on the environment, researchers are continuously trying to research and propose various alternative fuels. In the current study, the Biodiesel was produced from waste soyabean oil and utilized as a fuel in combustion-ignition engine. A four stroke, single cylinder and water-cooled, combustion ignition engine connected is connected with a dynamometer and its performance is checked with prepared Biodiesel. A mixture of waste soyabean oil with pure diesel is mixed with different proportions of blends such as 10%, 20% and 30% to conduct the experiments. Various experiments with different conditions were considered to identify the effect of prepared Biodiesel blends. The experiment results showed that among all blends of Biodiesel, the 20% blend of Biodiesel had given the best results for maximum considered parameters. Such as at highest load of 15 kg, the Brake thermal efficiency obtained maximum as 22.45%, 21.8%, 19.8 and 16.6% for 20%, 10%, pure diesel and 30% blend of Biodiesel. It can be inferred from the experimental investigation suggests that the blended Biodiesel may be considered as an alternate fuel in a four-stroke, single-cylinder diesel engine without any modification in the existing engine. The obtained experimental results may be further utilised to perform the various analysis to enhance engine working conditions.

Bald eagle search optimization on dual fueled reactivity controlled combustion ignition based engine characteristics by altering low reactive fuels

AbstractIn conventional diesel engines, the reactivity controlled combustion ignition (RCCI) systems find to be offer better emission and engine performances. The main aim of this work is to study and enhance the emission, combustion, and performance characteristics of the RCCI based diesel engine. In the present work, we compare and optimize the characteristics of the diesel engines when using methane added hydrogen and methanol fuels as low reactive fuels (LRF). The diesel and dimethyl ether added biodiesel (spirulina microalgae) are used as high reactivity fuels (HRF) with six different proportion rates. In this, initially, the experimental results are investigated by using methanol as LRF with HRF fuel, and better blend proportion is optimized by using bald eagle search optimization (BESO) performed in the Matlab platform. Then, the methane content added hydrogen is used as LRF with the optimized HRF fuel combinations. Finally, from both cases, the optimized experimental characteristics are predicted with the help of the Elman recurrent neural network based BESO. In which, the hydrogen gas contributed RCCI engine provide supreme engine characteristics such as 217.6 g/kWh of specific fuel consumption, 38.7% of brake thermal efficiency, 84.45 bar of cylinder pressure, and the CO2 and NOx emissions are 539.2 g/kWh, and 1020 ppm. The result reveals that the proposed predicted results are superiorly validated the experimental outcomes with minimal errors.

The combustion performance and kinetics of Saray-Thrace region coal: The effects of particle size and heating rate

This research aimed at understanding the effects of particle size and heating rate on combustion characteristics and kinetics of Saray-Thrace region coal by performing thermogravimetry (TG-DTG) analysis. The TG-DTG curves revealed two main reaction regions for each heating rate studied (5, 10, and 15 °C/min, particularly the evaporation of moisture and carbonization stages. The reaction intervals extended while the corresponding peak and burn-out temperatures increased as the heating rate was increased. Furthermore, a slight delay occurred in burn-out temperatures while the peak temperatures mostly increased with increased particle size, which is correlated with the decrease in surface area. On the other hand, the average mass loss percentages in carbonization stages mostly increased with increased particle size. Similarly, the combustion performance and reactivity of coal samples, which were evaluated through the values of combustion performance index (S), maximum reactivity (Rmax), and ignition index (D), suggested that the larger the particle size and the higher the heating rate, the better the combustion activity. The kinetic analysis of coal samples was also performed using model-free (iso-conversional) methods, particularly the Ozawa - Flynn - Wall (OFW) and Kissinger - Akahira – Sunose (KAS). The corresponding average activation energy (Ea) range of different size coal samples varied within the range of 62.1–191.8 kJ/mol, and the lowest Ea found for the largest particle size coal sample, supported the ignition performance and reactivity results.

Enhanced Hydrothermal Carbonization of Spent Coffee Grounds for the Efficient Production of Solid Fuel with Lower Nitrogen Content

As an increasingly abundant lignocellulosic biomass with high moisture content, spent coffee grounds (SCG) are an ideal feedstock for hydrothermal carbonization (HTC). The few examples that have converted SCG into a solid fuel hydrochar have yet to address the char’s prohibitively high nitrogen content (∼3 wt %)–a barrier to commercialization due to NOx emission regulations. In this work, an alkaline pretreatment is presented that reduces the N content prior to carbonization under regimes optimized for maximum calorific value (HHV), energy yield, and a conflation of both fuel properties. Characterization of hydrochars and secondary chars, the extractable volatile phase, revealed the highest calorific value for the secondary chars (max HHV = 40.69 MJ/kg) and a minimum N content of 0.1 wt % in hydrochars derived from the alkali pretreated feedstock. Char thermal stability and oxidative reactivity were also determined, with pretreated primary chars exhibiting superior combustion reactivities, ignition, and burnout temperatures. Management of HTC process water is both an environmental and operational challenge due to the presence of phytotoxic organic components and the energy expenditure associated with heating large volumes of water. To this end, the process water was recirculated for up to five cycles resulting in an increase in HHV, energy, and solid yield as well as compositional change of the char products.