Higher Heat Release Rate Research Articles

The Effect of the Fuel Location and Ventilation Factor on the Fire Dynamics of Informal Settlement Dwellings

AbstractThree full-scale experimental compartment fires are compared to investigate the effect of the fuel location and the ventilation factor on under ventilated thermally thin bounded ISO-9705 compartments. Wood cribs were used as the fuel load and the crib placement was varied between two locations (back and middle) to study the effect of the fuel location. Furthermore, the ventilation conditions were changed from a door and window (i.e., ventilation factor of 2.58 m5/2) to only a door (i.e., ventilation factor of 2.26 m5/2) for the scenario where the cribs were placed at the back of the compartment. The novelty of this work lies in its examination of the time to flashover, gas layer temperature, heat release rate, and external radiative heat fluxes, specifically considering the impact of fuel location and ventilation factor. It was observed that placing the fuel package in the middle of the compartment led to a longer growth phase, hotter gas layer temperature, a higher Heat Release Rate (HRR) needed for flashover ($$\dot{q}_{fo}$$ q ˙ fo ), and higher external radiative heat fluxes through openings. It was also found that, decreasing the ventilation factor decreased the heat losses and therefore the $$\dot{q}_{fo}$$ q ˙ fo . Decreased ventilation also affected the height of the neutral plane, as one would expect, and the shape of the external plume, but did not have significant effect on the temperature within the compartment, the walls of the compartment, and the external radiative heat flux.

Characteristics of fires in coal mine roadways and comparative analysis of control effectiveness between longitudinal ventilation and cross-section sealing

Enhancing ventilation velocity and constructing sealing walls are prevalent strategies aimed at managing fires in coal mine roadways. To assess the efficacy of these control tactics, this study investigates the fire characteristics with varying heat release rates (HRR) using a 1:10 experiment and numerical simulations. Results reveal that an increase in the HRR corresponds to a decrease in ceiling temperature, alongside an increase in both smoke back-layering length and critical velocity. Longitudinal ventilation proves effective in lowering ceiling temperature and inhibiting upstream smoke propagation from fire source, but it does not extinguish the fire, instead reducing downstream visibility and escalating risk downstream of fire. When the actual velocity exceeds 3.1 m/s, it effectively prevents smoke backflow in a fire of 10 MW. Cross-section sealing works by reducing oxygen levels within roadway to suffocate the fire. As the sealing ratio increases, flame inclination angle and burning time decline, whereas ceiling temperature rises. When it exceeds 75%, CO concentration sharply rises and fire enters the extinguishment phase, if ratio is 100%, fire with higher HRR are extinguished more quickly. This study provides valuable insights into roadway fire control: longitudinal ventilation aids personnel evacuation, while cross-sectional sealing effectively extinguishes fires in unpopulated spaces.

Fire behavior of hemp blocks: A biomass-based construction material

Hemp blocks, also known as hempcrete, are eco-friendly and sustainable construction materials composed of hemp, lime, and water. In this study, the fire behaviour and structural performance of hemp-based materials were experimentally investigated. Fire exposure scenarios using raw hemp shives, hemp blocks, and non-load-bearing hemp block walls were examined. Tests conducted include cone calorimeter, bomb calorimeter, standard furnace, heat-transfer rating inducing system (H-TRIS), and small-scale elevated temperature material tests. Hemp shives exhibit ignition with sustained flaming, a relatively high heat release rate (HRR), and a relatively low critical heat flux (CHF). However, the hemp blocks exhibited no flaming ignition, only smouldering combustion, and an HRR an order of magnitude lower. Hemp blocks and hemp shives produced minimal smoke. Hemp blocks charred, and associated discoloration zones have been documented. Tests indicate that limited structural capacity is lost up until 200 °C, whereas at 300 °C, the residual material strength is almost negligible. The hemp block walls maintained their structural stability and integrity for 2 h of standard fire testing. The ambient-temperature compressive strength of the hemp blocks was determined to be 1.0 MPa. This work is the first comprehensive study on the fire behaviour of hemp blocks and highlights their good performance, whereby they are likely to have a limited impact on fire risk in buildings. Plastered walls will have a fire performance exceeding those reported here.

Effects of hydrogen peroxide on the low-temperature ignition delay times of ethylene/air/Ar mixtures in an RCM

Hydrogen peroxide with strong oxidative activity has received increasing attention in the field of ignition and combustion enhancement. To further seek out its potential benefits in ignition, the effects of hydrogen peroxide on the ignition delay times of ethylene were experimentally investigated using a rapid compression machine and numerically analyzed via the AramcoMech 3.0. The experiments with different levels of hydrogen peroxide (0 – 7000 ppm) were performed at Pc = 3.33 MPa, Tc = 817.9 – 921.0 K, φ = 0.5 – 1.5, and a dilution of 45 mol% Ar. Experimental results showed that adding hydrogen peroxide can effectively shorten the ignition delay times, and extend the low-temperature limitations. The improving effect was proceeded by three stages (0 – 1000 ppm, 1000 – 4000 ppm, and 4000 – 7000 ppm) of different decreasing rates. Kinetic analyses revealed that adding hydrogen peroxide promoted the production of OH radical to highlight the H-abstraction reaction of ethylene, further accelerating the oxidation of vinyl to vinyloxy and then to formaldehyde. Moreover, higher heat release rates were obtained with the addition of hydrogen peroxide for its exothermic character. By the kinetic effects of hydrogen peroxide addition, the ignition delay times of ethylene/air/Ar mixtures were significantly decreased. However, with the increase of additive fraction, the growth rate of both heat release rate and rate of production of OH radical were slowed down, lessening the enhancement effect on the ignition delay times.

Injection strategy of methanol for high loads and low NOx emissions in a neat methanol LTC engine

Methanol is a low carbon and clean burning renewable fuel. Though low temperature combustion (LTC) of neat methanol results in almost no smoke with ultra-low NOx, the extremely low cetane number poses challenges. This experimental study demonstrates LTC of neat methanol at full load by combining direct and port injection of this fuel with controlled intake air temperature (IAT). The effects of important variables including IAT and port (premixed) and direct-injected methanol shares on combustion, performance, regulated and unregulated emissions were investigated. The timing of the direct-injected methanol had to be retarded with an increase in the premixed methanol share and IAT in order to limit the pressure rise rate without affecting the ITE. At high IATs, the premixed methanol burned first, followed by the directly injected methanol, at low IATs, these phases merged, resulting in a high rate of heat release. Employing the lowest possible IAT and the highest possible premixed methanol share led to high ITE. Increase in the MDIP to 450 bar was advantageous due to better fuel evaporation and enhanced combustion. Negligible smoke, very low NOx of 2.7 g/kWh, high ITE of 45% and unburned HC and methanol emissions lesser than 3 g/kWh could be achieved.

An engineering model for the pyrolysis of materials

Accurately representing the time dependent heat release rate of fuels is critical to performance-based design in fire safety applications. Existing simplified models either use average pyrolysis rates at different heat fluxes or do not account for the change in burning behavior at higher heat transfer rates. This paper presents the theoretical basis of a scaling-based pyrolysis model, S-Pyro. The model is based on the concept of maintaining the shape of a reference heat release rate per unit area curve but scaling the magnitude and time based on a dynamic thermal exposure. The model has been implemented in the computational fluid dynamics software Fire Dynamics Simulator (FDS). The model is validated with solid-phase only and multi-phase simulations of cone calorimeter experiments. The solid-phase simulations evaluated the capability of the model to predict the heat release rate per unit area of 149 materials tested at heat fluxes other than the reference flux. Multi-phase simulations of bench-scale fire experiments with a single material, Canada Pine and Spruce plywood, were used to evaluate the performance of the pyrolysis model in FDS. The model uncertainty was lower for high heat release rate materials, with the model uncertainty approaching the experimental uncertainty at higher burning rates.

Direct numerical simulation of NH3/air combustion with H2 addition under HCCI relevant conditions

In the present work, two-dimensional direct numerical simulations (DNS) of NH3/air turbulent combustion with H2 addition under homogeneous-charge compression ignition (HCCI) relevant conditions were performed to explore the ignition and combustion characteristics. Three hydrogen addition levels in the fuel were considered with molar fractions of 0.0 (pure ammonia), 0.1 and 0.8. The corresponding one-dimensional laminar flames were also simulated to provide reference solutions. The general combustion characteristics were first presented. It was found that turbulence and thermal stratification facilitate the ignition process. The ignition occurs earlier with increasing hydrogen addition levels and temperature fluctuations. After ignition, high heat release rate (HRR) occurs simultaneously over the entire domain with low temperature fluctuations while significant HRR occurs in narrow sheets with high temperature fluctuations. HRR is significantly enhanced in positive curvature regions of the cases with high hydrogen addition levels due to the preferential diffusion of H and other radicals. The combustion mode was examined based on the analysis of the displacement speed and species transport equation budget. The mean displacement speed is decreased with increasing temperature fluctuations and the budget analysis suggests that high temperature gradient facilitates deflagration. The reaction fronts are thinner with increasing H2 addition levels, and the combustion mode of deflagration is promoted. The effects of turbulence intensity on the flame structure and combustion mode were evaluated. The ignition occurs earlier and the area of the reaction front increases with increasing turbulence intensity. The magnitude of the temperature gradient also increases with increasing turbulence intensity, which facilitates the occurrence of deflagration. The turbulent flame structures were compared with the corresponding 0D ignition and 1D thermally stratified flame results, and it was found that the mean turbulent flame structure can be well approximated by 1D thermally stratified flames.

Investigating the influence of plastic waste oils and acetone blends on diesel engine combustion, pollutants, morphological and size particles: Dehalogenation and catalytic pyrolysis of plastic waste

Most research into the treats of plastic wastes have concentrated mainly on single-exposure pathways or products. These practices fail to acknowledge that the complications of carbon particles from engines are produced not only by diesel but by any plastic oils due to the vast amount of contaminants. With the potential to significantly weaken the impact of contaminants, the present study investigates the effects of dehalogenation and catalytic pyrolysis on plastic waste, as well as the risks associated with plastic oil blends on diesel engine. Different types of washing were conducted to effectively dehalogenate plastic waste. After pretreatment, odor compounds were analyzed using GC–MS. Subsequently, various types of pretreated plastic samples underwent catalytic pyrolysis with a 5:1 ratio of HDPE to Al2O3·2SiO2·2H2O. Differences in physico-chemical properties and hydrocarbon compounds of oils were determined. Experiments were performed using different fuel blends in a diesel engine under steady-state conditions, and their effects on combustion, emissions, morphology, and size particles were analyzed. The results show that sample B exhibited a lower toxicity level of 1,3-butadiene compared to other samples, while acetone and terpenes represented the second and third-highest emission levels in flakes, respectively. Sample C started to degrade at low temperatures (<300 °C) due to carbon addition from ethyl acetate solvent into the tertiary carbon chain of the flakes. DAP3 fuel achieved a higher reaction due to its degree of unsaturation and lower viscosity, resulting in the formation of smaller fuel droplets at high injection pressure and heat release rate (HRR). Higher emission levels were observed by DAP1 and D100, exceeding the Euro 5/6 standard limits. However, DAP3 fuel resulted in an average reduction of ∼17.14% and 21.86% in CO and smoke emissions, respectively, accompanied by a slight decrease in NOx and HC levels. Conversely, there were inconsistencies in the emission results observed with DAP2. Compared to D100, both DAP1 and DAP2 exhibited a significant accumulation and coarse particles in the PM10 forms at a peak of ∼83 nm. Whereas the DAP3 showed a smaller mobility Dp with a low nucleation particle peak, which was prone to absorb the unburned HC soot and later change to accumulation mode particles.

Characterisation of non-premixed, swirl-stabilised, wet hydrogen/air flame using large eddy simulation

The quest for decarbonisation of industry calls for phasing out fossil fuels and in some cases replacing them with green hydrogen in line with the Global Sustainable Goals. To that end novel hydrogen burners will be developed. In this work, the non-premixed combustion of steam-diluted hydrogen combustion is studied numerically in a swirl-stabilised combustor. The flame shape and stabilisation is discussed along with the effects of flow-field, stratification and temperature distribution on the flame. The characteristics of the swirl-stabilised flame is illustrated using several time-averaged and instantaneous contours of parameters including heat-release rate, local equivalence ratio and temperature. The effect of mixing and temperature distribution in the non-premixed configuration is studied quantitatively, subsequently identifying several flame regions. The combustion modes in these regions are also reported. Importantly, neither local hotspots nor flame flashback is observed in this steam-diluted hydrogen combustion.While a typical short hydrogen flame is observed near the centreline of the combustor, a weak V-shaped flame tail also co-exists. The heat-release rate in the flame tail is about two orders of magnitude lower than the main flame. Examining the flame structure using a normalised flame index showed that the combustion in the main flame is premixed-like while that in the main flame is non-premixed. The effect of the flow-field on the transport of fuel and air seems to influence this observation in the flame tail.The high heat-release rate regions of the flame comprised lean (ϕ<1), moderately hot (T = 800 to 1400 K) mixture. The flame tail region resulted from lean, hot (T >1500 K) mixtures. A flame region with rich mixture (ϕ = 1 to 2), featuring moderate heat-release rate, was found to be trapped between an axial fuel jet and the central recirculation region. All these flame regions had flameless combustion as the dominant mode of combustion. In particular, the flame tail region burned completely in the flameless mode. The lean and dominantly flameless combustion in the main flame regions are likely to lead to lower NOx.

Combustion, performance and emission discussion of soapberry seed oil methyl ester blends and exhaust gas recirculation in common rail direct fuel injection system

Research on alternative fuel production and compression ignition (CI) engine improvement techniques is more attractive recently. Waste-to-wealth concept refers that the utilization of the waste of soapberry seed and exhaust gas to run the common rail direct fuel injection type diesel engine by optimizing their contribution through experimental analysis is the novelty of this investigation. The recirculation of exhaust gas plays important role in improving the combustion in the engine, reducing the emissions, and improving the engine performance. Soapberry seed oil methyl ester economizes diesel consumption by mixing it into diesel. Transesterification is the method used to turn soapberry seed oil into biodiesel. In the common rail direct injection (CRDI) engine, a 10%, 20%, or 30% blend of soapberry seed oil methyl ester (SSOB) with diesel is utilized as fuel. For each mix, 10%–30% of the volume of SSOB is added to the rest of the diesel. Along with these fuel types, exhaust gas recirculation (EGR) is used from 10% to 30% to test and optimize the best combinations for CRDI engines. The experimental results show that pure diesel with EGR recorded high heat release rate (HRR) and brake thermal efficiency (BTE) at the highest load possible. The maximum BTE of the tested tracks is 26.83% because of better combustion, which was achieved with 10% EGR and a combination of 30% SSOB and 70% Diesel. The increase in EGR such as 30% in 30% of SSOB with 70% of Diesel blend produced reduced NOx emission (865 ppm), smoke opacity (13%), and hydrocarbon (HC) emissions (10 ppm) than diesel fuel because of the dilution and chemical effects during combustion. Accordingly, the present research reveals that a 30% of soapberry seed oil methyl ester blend with 30% EGR is recommended for engine usage with lesser emission with better combustion and performance characteristics.

Heat release rate of enhanced large-scale open oil slick fires with Outdoor Gas Emission Sampling (OGES) system

The Outdoor Gas Emission Sampling (OGES) system was developed to serve as an economical alternative to expensive industrial gas monitoring equipment. By establishing a sampling plane with four discrete sampling points along the radial direction of the smoke plume, the heat release rate (HRR) was measured for large-scale open oil slick fires. This newfound technique was particularly noteworthy during enhanced burns involving Flame Refluxer™ technology, where it is believed that partial premixing of the fuel and air by the apparatus resulted in a higher HRR than existing flame height correlations would suggest, evident by the HRR calculated using mass burning rate and gas analysis methods, which were in good agreement. Results from OGES show the potential of using point sampling within the plume regime to measure the HRR of fires that exceed the capabilities of conventional hood-based calorimeters, especially when it pertains to large-scale open burns.

A direct numerical simulation study on the structures and turbulence–flame interactions of a laboratory-scale lean premixed jet flame in cross-flow

In the present work, direct numerical simulation of a laboratory-scale lean premixed reacting jet in cross-flow was performed to explore the flow–flame structures and turbulence–flame interactions. A jet of lean premixed ethylene–air mixtures (equivalence ratio $\phi = 0.6$ ) was injected into a hot vitiated cross-flow. Both non-reacting and reacting cases were simulated. It was found that the reacting jet penetrates deeper in the cross-flow with a weaker shear layer compared with the non-reacting one. The wake of the non-reacting and reacting jet is characterized by vertical vortices and recirculation zones, respectively. As for the flame structure of the reacting case, the reaction intensity varies considerably in different flame zones. The heat release rate on the leeward side is higher than that on the windward side, but lower than that of the corresponding laminar flame. The analysis of the turbulence–flame interactions of the reacting case showed that the large local Damköhler number ( $Da$ ) related to reaction-induced dilatations results in an increased tendency of the scalar gradient to align with the most extensive strain rate, which is more evident in the regions with high heat release rate on the leeward side. Negative dilatation regions with positive tangential strain rate and negative normal strain rate are observed on the windward side. High positive dilatations appear on the flame front of the leeward side. The tangential strain rate is negatively correlated with the normal strain rate and curvature. Regions with a high local $Da$ on the windward side correspond with high positive curvature regions.

Effective utilization of waste pork fat as a potential alternate fuel in CRDI research diesel engine – Waste reduction and consumption technique

This work utilized the conventional transesterification process to convert waste pork fat into pork fat biodiesel. The produced biodiesel was meant to serve as a diesel fuel substitution for common rail direct injection (CRDI) diesel engines. Butylated Hydroxytoluene (BHT) as an antioxidant doping with waste pork fat biodiesel-diesel blend has not been analyzed in CRDI diesel engines. Therefore, to improve the ignition process and reduce the engine exhaust emissions in a research CRDI diesel engine, the BHT was employed to combine with diesel-biodiesel mixtures in this work. BHT antioxidants are partially mixed (BHT 50, 100, and 150 ppm) to improve the physicochemical qualities of test fuel and enhance the combustion process of diesel-biodiesel blends (B20). The antioxidant purity was analyzed by energy dispersive X-ray analysis (EDX), structures were analyzed by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) analyzer spectrograph was utilized to study the biodiesel chemical components. After mixing the BHT, the overall phase of the base fuel remained constant. The experiment outcomes revealed that the biodiesel had higher cylinder pressure than the other test fuels, and the BHT100 ppm blend had a higher heat release rate (HRR). B20BHT100 blend shows 3.98% higher brake thermal efficiency (BTE) at full load operation than pure biodiesel but lowered to diesel fuel. Biodiesel (B100) decreases the smoke opacity by 4.5% compared to diesel fuel. BHT has been incorporated into the biodiesel blend to minimize oxides of nitrogen (NOx) emissions at all loads. The B20BHT150 blend decreased NOx emissions by 5.06% more than diesel fuel at maximum load. Compared to pure biodiesel, the B20 blends reduce carbon monoxide (CO) emissions by 7.1% and hydrocarbon emission (HC) by 12.5%. This research found that adding BHT to biodiesel blends lowers NOx emissions with a slight impact on performance.

The use of multi-zone modelling for tunnel fires

This paper introduces the use of a multi-zone modelling approach for analysing smoke spread in tunnels. The approach suggested in this paper is based on an existing model, i.e., the Multi-Zone Fire model developed for large spaces. The Multi-Zone Fire model has been adapted and modified for tunnel fire scenarios by including features that consider longitudinal ventilation flow, tunnel gradient and tunnel section representations. An evaluation of the model has been conducted through benchmarking against experimental data from the BeNeLux tunnel experiments and the Runehamar tunnel fire experiments. The results from the Multi-Zone Fire model results were also compared against results from the Fire Dynamics Simulator. The results of the benchmarking exercise indicate that the multi-zone approach can be a time-efficient and useful tool for studying tunnel fire dynamics. The Multi-Zone Fire model performs well 50–200 m from the fire for heat release rates of 5–20 MW and moderate longitudinal ventilation flows. The model results are more conservative for the studied scenario with a higher heat release rate.

A Numerical Study on Spray Combustion and Emissions Characteristics of n-Heptane, Dimethyl Ether, and Their Blends in a Constant Volume Combustion Chamber

Abstract Dimethyl ether appears to be a better choice among various diesel alternatives due to its high cetane number and sootless combustion. However, the physical and chemical properties of dimethyl ether are very different from those of diesel. The physical properties influence spray formation and atomization characteristics, while chemical properties determine combustion and emission formation characteristics. Thus, fuel's physical and chemical properties significantly determine engine performance and emissions. In the present work, spray combustion and emission formation characteristics of n-heptane, dimethyl ether, and their blends (10, 25, and 50% dimethyl ether in n-heptane) were numerically studied in a constant volume chamber. Results show that the n-heptane spray combustion has the highest heat release rate with an intense premix combustion phase, whereas dimethyl ether spray combustion has the lowest heat release rate and shortest premix combustion phase. The magnitude of the premixed phase and heat release rate decreases with the increase in dimethyl ether mass fraction in the blends. Soot, carbon monoxide (CO), unburned hydrocarbon (UHC), and nitric oxide (NO) emissions decreased with the increase in the dimethyl ether mass fraction in the blends and were lowest for the dimethyl ether.

Control exhaust emissions of insulated diesel engine fuelled with biogas and cottonseed biodiesel

Gaseous fuels have many advantages than liquid fuels, as their calorific values of fuels are high, pollutants emitted by gaseous fuels are low and less dangerous when compared with liquid fuels. The drawbacks associated with use of vegetable oils in diesel engines such as high viscosity and low volatility can be reduced to some extent by converting them into biodiesel. However, they (biodiesel) cause combustion problems in diesel engine, due to their moderate viscosity, and hence call for low heat rejection (LHR) engine, which can burn low calorific value fuel, give high heat release rate and faster rate of combustion. The concept of LHR engine is to minimize heat loss to the coolant, thereby increasing thermal efficiency. LHR engine in this investigation consisted of ceramic coated diesel engine. They are many methods toinduct gaseous fuels such as port injection, carburetion technique, injection of gaseous fuel at the near endof compression stroke etc,. Investigations were carried out with biogas gas as primary fuel inducted by port injection and cottonseed biodiesel was injected into the engine in conventional manner, as India is second large producer of cottonseed oil in the world. Particulate matter (PM), oxides of nitrogen (NOx), carbon mono oxide (CO) levels and un-burnt hydro carbons (UBHC) are the exhaust emissions from a diesel engine. They cause health hazards, once they are inhaled in. They also cause environmental effects like Green-house effect and Global Warming. Hence control of these emissions is an immediate effect and an urgent step. The pollutants of PM, NOx ,CO and UBHC were determined at full load operation of the engine with varied injection timing such as recommended injection timing and optimum injection timing. NOx levels were reduced with provision of exhaust gas recirculation (EGR) at optimum flow rate of 10%. The maximum induction of biogas with conventional engine (CE) was 35% of total mass of biodiesel as full load operation, while it was 45% with LHR engine. Particulate emissions were determined by AVL Smoke meter, while other emissions were measured by Netel Chromatograph multi-gas analyzer at full load operation. These pollutants were drastically reduced with induction of biogas and further reduced with advanced injection timing. NOx levels drastically reduced with EGR.

Thermal behavior of diesel, honge oil methyl ester and ITS B-20 blend in atmospheric air and oxygen

ABSTRACT Thermal behavior of honge oil methyl ester (HOME) and its B-20 blend (20% HOME and 80% diesel) is examined by performing calorimetric experiments at 10°C/min heating rate in atmospheric air and oxygen medium. Thermogravitometry (TG) curves indicate two phases of decomposition for diesel and three phases for biofuel. Combustion reaction favors in oxidative atmosphere causing reduction in fuel preparation stage and increase in premixed burning phase reducing peak temperature of combustion and increasing enthalpy with high heat release rate. B-20 blend performance is similar to diesel with combustion index and intensity of combustion and is thermally stable with high offset temperature confirming more combustion duration. Blend of diesel lowers activation energy in initial stage of combustion process, whereas reverse trend is observed in final stage. Ignition index (Di) in air for diesel, HOME, and its B-20 blend is reduced by 70.11%, 34.92% and 42.80% respectively. Burnout index (Db) in air for diesel and B-20 blend reduced by 72% and 61% respectively whereas it increased by 28.5% for HOME. Combustion index (S) is more in air for HOME and its blend. Improved intensity of combustion is observed for diesel and B-20 blend in oxygen whereas reverse trend is observed for HOME.

Injection system modification and optimization for performance enhancement and emission reduction in a light-duty diesel engine fuelled by biodiesel-water emulsion

In conventional diesel engines, adding water to carbon–neutral biodiesel simultaneously reduces nitrogen oxides (NOx) and smoke emissions whilst improving engine performance. However, such investigations reported in the literature are conducted with engines equipped with a mechanically actuated fuel supply system lacking flexibility in the injection schedule. The present investigation aims at modifying and optimizing an existing mechanical fuel injection system to an electronic common rail injection (CRDi) system for utilizing biodiesel-water emulsion. A light-duty diesel engine's performance and emission characteristics with the modified CRDi system operated with biodiesel-water emulsion is compared with the mechanical injection system. The formulated Karanja biodiesel and water emulsion contained 18 % water, and 2 % of the raw oil was utilized as the stabilizer for the emulsion. The results show that the CRDi system results in lower peak cylinder pressure, higher heat release rates, and retarded combustion phasing for all the tested fuels compared to the mechanical injection counterpart. Compared to diesel with the mechanical injection system, biodiesel-water emulsion with CRDi system reduced fuel consumption and increased thermal efficiency by 30 % and 14 %, respectively, at 5.08 bar brake mean effective pressure (BMEP). The NOx emissions for the emulsion were similar to diesel with the mechanical injection system, whereas a decrease of 29, 30 and 10 % was observed for emissions of smoke, unburned hydrocarbon (HC) and carbon monoxide (CO), respectively. The current investigation reveals that utilizing biodiesel-water emulsion with a flexible injection system reduces engine exhaust emissions while simultaneously improving the performance characteristics.

Investigation and optimization of solidification performance of a triplex-tube latent heat thermal energy storage system by rotational mechanism

In this paper, the rotation mechanism is applied to a triplex-tube latent heat thermal energy storage system for the first time. Numerical simulation is used to study the effect of rotation on the solidification performance of this system, and the accuracy of the numerical model is verified experimentally. Firstly, the evolution of the liquid phase, the total amount of heat energy released, and the rate of heat energy released in the solidification process of the thermal energy storage system without rotation and at different rotational speeds are compared and analyzed. It is found that the solidification time of the system at 1 rpm is reduced by 83.85 % and the heat release rate is 4.98 times higher than that at the no-rotation state. It shows that the incorporation of a rotational mechanism can effectively reduce the solidification time and increase the heat release rate of the system. Then, the internal dynamic temperature/flow rate response is used to investigate the change in the heat transfer mode of the solidification process by the addition of rotation and the improvement of the phenomenon of difficult solidification zones, which improved the internal temperature uniformity and thus the solidification behavior. By response surface method, the geometric factors of the heat storage system (fin length, fin width, fin angle) are analyzed by multiple factors. The function of the optimized target (solidification time) on each variable is fitted, and it is found that the fin length had the most significant effect on the optimized target. Finally, the effect of relevant physical parameters on the solidification process and heat release of the thermal energy storage system is investigated. To ensure low solidification time and high heat release rate, this study recommends that the temperature difference between phase change material and tube wall is higher than 25 K. This paper also proves the feasibility and superiority of copper fin/tube wall material.

Fire spread along vertical greenery systems from window ejected flame: A study based on a fire dynamic simulator model

Recent studies have shown that, poorly maintained vertical greenery systems (VGS) have a high fire risk and a tendency to cause very high heat release rates (HRR) in a case of fire. High HRR in materials often results in rapid fire spread in upward orientation. This study used numerical fire simulations with computational fluid dynamics (CFD) to investigate the fire spread along a VGS. The fire simulations were conducted in fire dynamic simulator (FDS) using the pyrolysis model that was specifically developed for vegetation. In FDS, the fire was initiated as a room fire of 1 MW followed by a window ejected flame, which ignited a 12 m tall and 9 m wide VGS. Fire spread along a VGS was modelled with four different moisture contents (MC) and four different packing ratios (PR) of the vegetation fuel bed. The different MCs represented regularly and scarcely watered vegetation, while different PRs represented different bulk densities of the vegetation in the VGSs. The fire spread rate was increased when both the MC and PR were decreased. The rate of fire spread in the upward orientation, which is the most hazardous mode of fire spread, was found to increase by 469.8% when the MC was decreased from 80% to 10%, and by 207.1% when the PR was decreased from 0.5 to 0.1. The results are helpful in understanding the design of a VGS with an optimum level of vegetation density and maintaining the vegetation fresh and alive to minimise the fire hazard. • Numerical simulations are conducted with a fire dynamic simulator model. • Moisture content (MC) and packing ratio (PR) of vegetation were varied. • Lower MC and PR of vegetation increase the fire spread rate. • Fire spread is notably faster in the upward direction over green wall. • Keeping vegetation fresh and lush is vital to reduce the fire risk.