Increased Heat Release Research Articles

Study on the Effects of EGR and Spark Timing on the Combustion, Performance, and Emissions of a Stoichiometric Natural Gas Engine.

This paper involved conducting an experimental investigation on the effects of exhaust gas recirculation (EGR) and spark timing on the combustion, performance, and emission characteristics of a China-VI heavy-duty, natural gas engine fueled with high-methane content. The results showed that increasing the EGR rate extends the spark timing range and slows the combustion. This then increases ignition delay, prolongs combustion duration, and decreases heat release rate. Peak in-cylinder pressure (PCP) and indicated thermal efficiency (ITE) initially increase because of higher boost pressure with increasing EGR rate. However, as EGR rate increases further, PCP and ITE begin to decrease because of the deviation of combustion phasing. Lower in-cylinder temperature caused by higher EGR rate may cause nitrogen oxide (NOx) emissions to reduce significantly, while total hydrocarbon (THC) and carbon monoxide (CO) emissions increase, and THC emissions could increase exponentially at high EGR rates. In-cylinder pressure, temperature, and heat release rate increase with early spark timing, but the rate of increase is reduced at higher engine speeds. Early spark timing causes THC and CO emissions to increase at part-load conditions, whereas there is little change at full-load conditions. NOx emissions also increase with early spark timing because of the higher in-cylinder temperature.

An experimental and numerical study of polyoxymethylene dimethyl ethers on a homogeneous charge compression ignition engine

ABSTRACT Polyoxymethylene Dimethyl Ethers (PODEn) are a kind of high-activity and promising soot-reduction additive fuel. The effects of enhanced intake charge temperature (Tin ) and low fuel-air equivalence ratio (Φ) on the combustion and emission characteristics of PODE2-8 were captured on a homogeneous charge compression ignition (HCCI) engine. Meanwhile, a numerical study using Chemkin was conducted to investigate the effects of Tin on the combustion characteristics of PODE3. The results indicate that with the increase of Tin , rate of production (ROP) of CH2O and OH radicals and rate of exothermic reactions related to H- and O- species are greatly promoted, which result in a highly reactive atmosphere, advanced ignition timing (IT) and increased heat release rate (HRR). Typical two-stage auto-ignition behavior is also observed in lean PODE2-8 HCCI at high Tin . The enhanced Tin can promote the rate of CO-to-CO2 and decrease combustion duration (CD), which eliminates the third HRR oxidation peak. At Φ = 0.143, the peak in-cylinder pressure has increased by about 40% and the combustion duration (CD) has decreased by nearly 25% when Tin is from 80°C to 140°C. Moreover, for all test cases, NOx, HC, and CO emissions are lower than 15 ppm, 100 ppm, and 1%, respectively. Φ has a slight effect on the ignition timing of low temperature (ITL ) but an obvious effect on the ignition timing of high temperature (ITH ). With an increase of Φ, CO emissions decrease, HC emissions decrease first and then increase, and NOx emissions slightly increase. This research reveals that the combustion and emission characteristics of PODEn are sensitive to Tin , PODEn with enhanced Tin can form a chemical atmosphere with high-activity radicals.

An experimental study on the transition velocity and smoke back-layering length induced by carriage fire in a ventilated tunnel

Smoke is one of the important causes of tunnel fire casualties. The critical velocity and smoke back-layering length are important parameters of smoke control in the tunnel. This paper focused on experimentally studying the characteristics of the critical control parameter (such as, critical velocity, transition velocity) and smoke back-layering length induced by carriage fire in the longitudinal ventilated tunnel, which has not been quantified in previous studies. Overall, many repeatable test conditions were involved on different fire heat release rate (HRR), the longitudinal ventilation velocity and opening sizes. It is found that, when the fire heat release rate in the tunnel is small, the critical velocity increases with the increasing heat release rate. The critical velocities will no longer change when the fire heat release rates further increases to a certain value. The relationship between dimensionless smoke back-layering length and critical velocity is piecewise function. With the longitudinal ventilation velocity increasing to a certain value, the smoke back-layering length will become not sensitive to variations with the longitudinal ventilation velocity any more. So, for this part, the new parameter called “transition velocity” implies that the dimensionless smoke back-layering length changes slowly with the dimensionless critical velocity. Then, the dimensionless correlation of smoke back-layering length and transition velocity induced by carriage fire in ventilated tunnel was proposed.

Temperature evolution from stratified- to well-mixed condition inside a fire compartment with an opening subjected to external wind

It is well recognized that with increase in heat release rate (HRR), the compartment fire evolves from stratified- (hot gas in upper part and cool air in lower part) to well-mixed (uniform temperature) condition. However, such evolution for a fire compartment with an opening subjected to external wind, with a complex flow buoyancy-wind interaction, has not been quantified in the literature despite of its practical significance. The present study investigated experimentally the evolution of temperature spatial non-uniformness, namely the temperature difference between the upper- and lower part, inside a fire compartment with flow developing from stratified- to well-mixed condition with one opening subjected to external wind for various opening dimensions, HRRs and wind speeds with total 310 conditions. It was found that this temperature difference first increased then decreased with increase in HRR; and the HRR for the turning point (with maximum temperature difference) was found to be 0.6 times of the critical HRR for flame ejection under no wind condition. Such temperature difference, as well as its maximum value that can be reached, decreased with increasing of wind speed. A non-dimensional model was proposed based on physically the competition of the wind vent-mixing effect with the buoyancy effect inside the compartment and such competition at the opening, as well as the heat release/loss balance inside the compartment. The temperature difference between the upper- and lower-part of the compartment was found to be well represented as a function of wind Froude number at the opening and that inside the compartment, heat release to heat loss ratio and HRR. These new findings and the proposed non-dimensional model provide the basis for understanding fire growth and temperature evolution inside a compartment under complex buoyancy-wind interaction.

Investigation of kerosene supersonic combustion performance with hydrogen addition and fuel additive at low Mach inflow conditions

Stable and efficient combustion is critical for low Mach starting stage of Dual-Mode Scramjet. In this paper, basic experimental validation and three-dimensional simulation of hydrogen addition and fuel additive effects on kerosene supersonic combustion performance were conducted under flight Mach 3.8 inflow conditions. Hydrogen addition was injected independently and the additive effects were simulated by the method of reducing activation energy. The simulation results are well-agreed with the experimental measurements from hydrogen addition cases and 20%-vol additive cases, validating the numerical method and models employed. The relative activation energy needed for well simulating 20%-vol additive effects tends to be higher than the theoretical prediction and also different by equivalence ratios. The heat release is intensified by either hydrogen addition or fuel additive, resulting in higher temperature-rises and pressure-rises, and more OH radicals for combustion enhancements at low-temperature conditions. An appropriate small amount of hydrogen addition (ERH < 0.08) can promote kerosene pre-evaporation and combustion heat release to achieve higher combustion efficiency; a large amount of hydrogen addition exhibits a competitive mechanism with kerosene cracking and CO oxidation conversion, also reduces the degree of diffusive mixing. Either the same small amount of hydrogen addition or fuel additive, more significant enhancement effects can be observed at the lower equivalence ratio of kerosene, due to the increased heat release induced flame stabilization and combustion mode transition. Compared with hydrogen addition, combustion efficiencies with increasing additive effects are increased monotonously to a higher level when kerosene equivalence ratio of ERK = 0.53, whereas lower efficiencies when ERK = 0.43.

Pyrolysis characters and fire behavior of bus ceiling materials

The pyrolysis characters and fire behavior of ceiling materials have a great impact on the fire retardant of the whole bus because the fire might spread along the ceiling. This study investigated the pyrolysis characters of five plastic ceiling components with TG tests at four heating rates, and then, the kinetic parameters were calculated with Kissinger method, Friedman method and an advanced isoconversional Vyazovkin method. The obtained kinetic parameters were also validated by reconstruction of conversion curves. Finally, the flammability of each component from three ceiling materials was estimated using PCFC, and the fire behavior of three ceiling materials was investigated with cone calorimeter at different heat fluxes. Results show the pyrolysis characters of surface material could explain the early stage fire behavior of ceiling materials. The ignition and fire resistance were also highly dependent on the properties of surface materials. A transition between limited and more fierce combustion occurs at some heat flux for three ceiling materials. This property was related to the composition and structure of ceilings. Below this transition heat flux level, only the surface layer of ceiling was ignited and the fire load was limited. Above this level, the underlying layer was involved in combustion and leads to a sharply increased heat release. These results suggest that the flame retardant of surface material was important to promote fire retardant of the whole ceiling. Moreover, the obtained parameters can be used for predicting fire propagation in bus ceiling.

Experimental and numerical studies on dynamic thermal performance of hollow ventilated interior wall

The system integrating hollow ventilated interior wall (HVIW) with solar air collector in residential buildings on Tibetan Plateau facilitates in reducing heating energy use and improving nighttime thermal comfort. In this paper, dynamic thermal performance of HVIW is investigated by experiments and numerical simulations. Experimental results of 3 cases show that heating from the interior wall to the room space lasts during the whole day, and the heat released during the non-ventilation time accounts for more than 40% of the total heat input. Numerical model of this HVIW is validated by experimental results and used to study the influencing factors. Numerical results indicate that the baffle effectively reduces the air short circuit and improves the heat exchange inside the air channel, but resulting in a higher pressure drop. The thicker air channel is averse to the heat transfer inside the channel, while the thicker concrete wall is beneficial to the heat transfer with the increased heat release during the non-ventilation time. With the same ventilation time, the varying inlet air temperature and the intermittent operation significantly increase the total heat released during a whole day and the non-ventilation time. Study of influencing factors in this paper is beneficial to the design of HVIW.

Influence of injection parameters on combustion, gaseous emissions and particle size distribution of a CRDI diesel engine operating with PODE/diesel blends

This study deals with the experimental research on combustion process, gaseous emissions characteristics and particle size distributions of a high pressure common-rail direct injection (CRDI) diesel engine operating with PODE/diesel blends at different injection pressures (80 MPa, 90 MPa and 100 MPa) and injection timings (0.5°CA ATDC, 2.5°CA ATDC and 4.5°CA ATDC). The testing fuels were neat diesel, PODE/diesel blends with PODE volume fractions of 10% and 20%, which were marked as P0, P10 and P20 respectively. The results show that the maximum combustion pressure and peak value of heat release rate increase with the increment of injection pressure while the combustion pressure decreases slightly with the delay of injection timing. The CO, HC and soot emissions of the blended fuels decrease obviously with the increase of injection pressure, while the NOx increases, in which the increasing extent of NOx by fueling P10 is smaller than those of P0 and P20 fuels. Even though CO, HC and soot of the three fuels increase with the delay of injection timing, the NOx emissions decrease and the gaseous emissions of P10 fuel are still less affected by injection timing. The peak values of particle number concentration curves of the blends decrease with higher injection pressure, among which the proportion of accumulation particles decreases and the proportion of nucleation particles increases. The particle number concentration increases with the delay of injection timing for each testing fuel, but the geometric mean diameter (GMD) of P10 particles is little affected by the injection timing. Also, the particle diameter corresponding to the peak concentration for each testing fuel decreases with the increase of injection pressure and the advance of injection timing.

The optical investigation of hydrogen enrichment effects on combustion and soot emission characteristics of CNG/diesel dual-fuel engine

Compressed natural gas-Diesel dual-fuel combustion mode, the partial replacement of diesel fuel with cleaner fuel, is one of the most important strategies to achieve clean efficient combustion. However, low substitutions conditions face unstable combustion and high emission issues. Thus, the current work investigated the effect of hydrogen blending in natural gas on the combustion and soot emission characteristics experimentally in an optical engine. An optical diagnosis study of its performance, combustion flame development, and soot concentration distribution was conducted at various hydrogen volume rates (0%, 30%) and main injection timing (13°CA BTDC, 10°CA BTDC, 5°CA BTDC). In-cylinder flame images were captured by a high-speed camera and further processed to obtain flame characteristics as well as soot distributions. The results showed that the effect of hydrogen blending is mainly reflected in a change of ignition delay period and more ignition points at the initial combustion stage which improves combustion stability. When hydrogen is added, flame propagation speeds up, the flame distribution is more extensive especially in the first stage combustion, the heat release rate and pressure rise rate increase accordingly. Besides, soot emissions considerably decreased in the central region of the cylinder, especially during the first stages of combustion. When the injection advance angle is large, adding hydrogen results in the ignition delay period is extended, more premixed flames appear, and the maximum pressure increases. When that is small, adding hydrogen shortens the ignition delay period, but the poor diesel atomization results in diffusion combustion.

Calibration of idling characteristics for Lemon Peel Oil using Central Composite Design in light commercial vehicle diesel engine

Lemon Peel Oil is a clean and sustainable biofuel that has shown promising results under varying driving conditions. Growing vehicle density globally makes road congestions a common sight where the engines operate under idling conditions accounting for massive fuel wastage and severe emissions. However, considering the frequent occurrence of idling and the damage caused by it, the need to calibrate engines to utilise Lemon Peel Oil under idling conditions for addressing the issues of fuel shortage and pollution is observed. Hence, this work utilises a systematic experimental approach to analyse the potential of a 20% (vol/vol) blend of Lemon Peel Oil in diesel and compares it with conventional diesel for idling conditions. The systematic experimentation is determined using the Response Surface Methodology coupled with Central Composite Design on a Common Rail Direct Injection Engine Setup. The potential of the biofuel blend is analysed by mathematical modelling of various tests conducted. At optimal idling calibrations, 42.1% drop in smoke emissions and 16% reduction in Carbon Monoxide with an increase of 5.25% in Carbon Dioxide is reported. The slightly reduced heating value of the fuel caused a 10.18% reduction in thermal efficiency and a 21.24% increase in Specific Fuel Consumption. The 2.43% increase in peak pressure and the 4.6% increase in Heat Release Rate further suggests this biofuel blend possesses superior combustion characteristics and is a cleaner fuel. Hence, the potential of Lemon Peel Oil with optimized engine parameters is determined for the idling condition.

Effect of anisole addition to waste cooking oil methyl ester on combustion, emission and performance characteristics of a DI diesel engine without any modifications

Energy recovery and utilization from waste presents an attractive alternative solution to compensate fossil fuel demands and reduces the risk of environmental hazards. The present study aims to investigate, the effect of increasing anisole fraction in the biodiesel extracted from waste cooking oil in a diesel engine. Tests were performed by blending anisole with waste cooking oil methyl ester up to 30% vol. and the results were compared with baseline diesel and biodiesel operation. The results reveal that, increasing the anisole content in biodiesel prolongs the ignition delay period. The in-cylinder pressure and heat release rate increase with higher anisole fraction. Among the test fuels, W90A10 blend shown 1.6% better BTE than biodiesel. The NOx emission was lowest when the engine is operated with W90A10 blend, at peak load, it decreased by 17% and 11% against diesel and biodiesel operation. The smoke opacity for neat biodiesel was highest and the addition of anisole suppressed the soot formation tendency of the biodiesel significantly. HC and CO emissions are generally high when the engine is operated with biodiesel. Blending anisole with biodiesel had a positive effect on both HC and CO emissions. From the findings, it is concluded that waste cooking oil methyl ester blended with 10% by vol. of anisole can be effectively utilized in diesel engine applications with lower emissions.

Evaluation of heat release caused by low-temperature oxidation of heavy oil and its SARA fractions under isothermal conditions

During in-situ combusiton, the oils in most of the area before the combustion front encounter low-temperature oxidation (LTO) reactions under relatively isothermal conditions in a long time, and heat release of LTO significantly influences the quality of formed fuel. This work is aimed at examining the heat release of LTO of one Xinjiang heavy oil and its saturates-aromatics-resins-asphaltenes fractions using isothermal high-pressure differential scanning calorimetry tests. Furthermore, the widely-accepted LTO reaction pathways of hydrocarbons are summarized. The results indicated that the Xinjiang heavy oil, aromatics, and resins experienced the increased heat release from 200 to 250 ℃ and from 300 to 350 ℃ due to their elevated oxidation rate, and the decreased heat release from 250 to 300 ℃. Thus, to build a stable combustion of the oil, it is key to overcome the action energy barriers between 250 and 300 ℃.

Feasibility study of employing diverse antioxidants as an additive in research diesel engine running with diesel-biodiesel blends

This study examines the prospect of utilizing biodiesel from non-edible, waste seed derived from grapefruit. The prepared biodiesel was intended to replace the diesel fuel in a research diesel engine. Two antioxidants namely BHA (Butylated Hydroxyanisole) and BHT (Butylated Hydroxytoluene) are partially blended to enhance the ignition patterns of diesel/biodiesel blends. 30% volume of grape-seed biodiesel (BD) is blended with 70% volume of diesel and identified as base fuel. 10% volume of two antioxidants is equally blended to base fuel to enhance its physic-chemical properties. Upon blending the antioxidants, no change in phase was observed for base fuel. Performance results found that BHA and BHT addition lowered 1.2–1.4% of BSFC, and improved 0.7–1.1% of BTE of diesel/biodiesel blends respectively. Besides, BHA and BHT inclusion improved the physio-chemical properties of diesel/biodiesel blends and produced a prominent increase in In-Cylinder Pressure (ICP) and heat release rate (HRR). Emissions results revealed that BHA and BHT addition lowered 1.8–2.1%% of CO, 2.2–2.6% of HC of diesel/biodiesel blends. Further, a higher cetane number of BHA and BHT improved the combustion and lowered smoke (2.9–3.4%) and NO (1.9–3.7%) emission for diesel/biodiesel blends.

Analysis of a diesel engine fueled with ternary fuel blends and alumina nano-additives at various combustion chamber geometries

The present study investigates the impact of various combustion chamber geometries in a direct injection engine fueled with diesel–biodiesel–ethanol blends mixed with alumina nano-additives, named as high-performance fuel (HPF). The HPF was subjected to various combustion bowl geometries including standard hemispherical chamber geometry (SG), shallow depth reentrant bowl geometry (CG1), toroidal reentrant chamber geometry (CG2), and toroidal chamber geometry (CG3). Performance results reveal that in comparison with the SG-HPF arrangement, brake thermal efficiency increased by 11.51% and brake-specific energy consumption decreased by 10.37% when using the CG2-HPF arrangement. For emmisions, CG2-HPF reduced carbon monoxide, hydrocarbon, and smoke emissions by 33.53%, 18.35%, and 14.37%, respectively, in comparison with SG-HPF. Regarding combustion, CG2-HPF resulted in a high heat release rate owing to the reentrant chamber profile of CG2 which improves the air–fuel mixture rate, atomization, and evaporation rate, resulting in more efficient combustion, increased cylinder pressure, and increased heat release rate. Thanks to the geometry of the reentrant profile, the turbulent kinetic energy of the fuel mixture is maintained and returned to the combustion zone. Thus, the stagnation of rich mixtures within the combustion zone tend to decrease. Overall, the CG2 geometry was found to be the optimum geometry profile for HPF, based on improved performance and combustion characteristics, as well as reduced exhaust emissions.

Effect of nozzle hole geometry on the operation of kapok biodiesel in a diesel engine

The strive for mitigation of toxic pollutant emissions and carbon footprints has resulted in the incursion of many renewable alternate fuels, produced from bio-derived sources. Amongst them, biodiesel, an ester of vegetable oil, has amassed immense popularity and interest for diesel engine applications. In order to operate higher blends of biodiesel in a diesel engine, engine design modification strategies are essential. This study investigates the effect of nozzle hole geometry on the characteristics of a diesel engine fueled by biodiesel. Based on this modification, the number of nozzle holes was increased from three to five and the engine characteristics were examined for the higher blend B50 (50% kapok biodiesel + 50% diesel). Modifying the nozzle hole geometry resulted in improved combustion characteristics on account of expected enhanced fuel atomization and air/fuel mixing process. The experimental study revealed an increase in peak heat release rate and in-cylinder pressure of 32.5% and 10%, respectively, for B50 when the number of nozzle holes was increased from 3 to 5 at full load condition. Furthermore, the ignition delay was shortened with a shorter burn duration (improved combustion rate) as the number of nozzle holes is increased. The modification of nozzle hole geometry offers the benefit of improved engine performance with the increase in brake thermal efficiency of 6.1% for 5 hole nozzle geometry when compared to 3 hole nozzle geometry at full load condition. Finally, from the emissions front, HC, CO, and smoke decreased with the increase in the number of nozzle holes at the penalty of increased NOX emission.

Experimental investigation and numerical assessment the effects of EGR and hydrogen addition strategies on performance, energy and exergy characteristics of a heavy-duty lean-burn NGSI engine

In order to investigate the influences of hydrogen addition and exhaust gas recirculation (EGR) strategies on performance, combustion, emissions, energy and exergy balance of a lean-burn and high compression ratio (CR) (13.6) natural gas spark ignition (NGSI) engine fueled with 99% methane content is tested on the engine bench under different hydrogen contents. A corresponding 1D GT-Power simulation model is built and validated according to experimental data. In the first stage, both peak cylinder pressure (PCP) and peak heat release rate (HRR) increase with the hydrogen addition but decrease with increased EGR ratio. Besides, EGR addition will retard the effect of various hydrogen contents on performance and combustion of the engine. In the second stage, the NOx emissions increase with hydrogen enrichment but decrease with the increase of EGR rate due to the variation of in-cylinder temperature, which emphasizes effective method of EGR addition strategies to reduce the NOx emissions on the lean-burn NGSI engine fueled with natural gas-hydrogen (HNG). Finally, the change trends of exergy terms are similar to their corresponding energy, but the percentages of heat transfer exergy and exhaust exergy are about 7.05 and 2.61 times lower than their corresponding energy. Furthermore, the simulation model and data in the paper can be applied to evaluate and optimize the energy distribution and performance by changing different technologies, strategies and fuels in the future. What is more, the analysis of the energy and exergy balance can provide a new thought for the future research to improve engine’s performance.

Effect of fuel bed size and moisture on the flammability of Eucalyptus saligna leaves in cone calorimeter testing

The effect of the fuel bed size and moisture content on the flammability of Eucalyptus saligna leaves was investigated using the Cone Calorimeter. Tests were carried out using modified cylindrical shape “closed” sample holders with various diameters. This specific type of sample holder did not allow mass transfer through the sample boundaries and minimised the convective heat transfer from the sides. Leaves were conditioned to three different states, i.e. oven-dried, natural-dried, and fresh samples resulting in different values of moisture content. Flammability criteria such as time to ignition, burning rate, heat release rate, and heat of combustion were measured and analysed in every test condition. The results show an evident influence of the sample diameter, as well as fuel moisture content, on the flammability. The values of burning rate and heat release rate increase at a diameter range of 5–12.5 cm and slightly decrease until the 17.5 cm diameter. Thus, the sample size used in the cone calorimeter must be explicitly considered to get comparable results. The study also shows the importance of adequate testing method and sample preparation in small-scale flammability study of wildland fuel.

Experimental and numerical study of pool fire dynamics in an air-tight compartment focusing on pressure variation

The present paper studies the fire-induced pressure evolution in an air-tight compartment. Two cases with different sizes (i.e., 0.3 m × 0.3 m and 0.5 m × 0.5 m) of square methanol pool fire are considered. Repeated tests were performed for each case, leading to a total of four fire experiments. The leakage of the compartment is measured under different pressure conditions in order to obtain the relationship between the leakage and the pressure increase. The pressure inside the compartment reaches peak values of 133 Pa and 697 Pa for the small and the large pool fire, respectively. Simulation results using the Fire Dynamics Simulator (FDS) 6.5.3 match well with experiments. The simulated leakage flow rates, which reach values up to 65 m3/h and 200 m3/h, respectively, depend on the pressure variation and leakage settings. The pressure rises strongly in the growth phase of the fire, in line with a rapid increase in fire heat release rate. The gradually increasing heat losses subsequently lead to a decrease in pressure.

Improving the thermal efficiency of a T-GDI engine using hydrogen from combined steam and partial oxidation exhaust gas reforming of gasoline under low-load stoichiometric conditions

Hydrogen (H2) addition is known to have features of increasing the laminar burning velocity (Di Sarli and Di Benedetto, 2007), the resistance of the flame to strain-induced extinction (Di Sarli and Di Benedetto, 2012, 2013), and also enlarging the operating window of stable combustion (Di Sarli, 2014). We experimentally investigated how to improve the thermal efficiency of a turbo gasoline direct injection (T-GDI) engine using H2 from combined steam and partial oxidation exhaust gas gasoline reforming under low-load stoichiometric conditions. During real driving, 4 and 6 bar brake mean effective pressure (BMEP) at 2,000 rpm are frequently used. Our experimental results show that reformed H2 improves the brake thermal efficiency (BTE) of T-GDI engines operating at 4 and 6 bar BMEP. Furthermore, the combustion speed (increasing heat release rate) and stability (reducing cyclic variation) were enhanced by reformed H2, making more heavy exhaust gas recirculation (EGR) operation. Combining steam and partial oxidation exhaust gas gasoline reforming with extra air injection to a reformer had a large effect on the fuel conversion efficiency of the reformer as the engine load decreased. Therefore, the BTE of the T-GDI engine with combined steam and partial oxidation reforming achieved further improvement over steam reforming only at 4 bar BMEP. Nitrogen oxide (NOX) emissions increased with reformed H2. However, on the basis of the improved combustion stability achieved using reformed H2, NOX emissions could be reduced further by using a higher EGR rate while enhancing the BTE.

Mass flow during fire experiments in a model-scale mine drift with longitudinal ventilation

ABSTRACT Fires in underground mines may cause dangerous phenomena to mining personnel. One of these phenomena is the throttle effect, reducing the mass flow. This paper investigates the nature of the throttle effect. Data was provided from fire experiments in a model-scale mine drift. With an increasing heat release rate the reduction in the mass flow will increase. An increasing ventilation velocity may initially cause a reduction of the mass flow. With a further increase of the flow velocity the mitigating effect of the forced flow will increase. A dimensional analysis resulted in an equation where the mass flow reduction could be reasonably well described. It was found that the flow velocity had a weak effect on the mass flow reduction. Nevertheless, the flow velocity influence the initiation of the reduced mass flow. A full-scale flow velocity of 3.5 m/s was found to prevent the throttle effect for typical fires underground.