Fuel Mass Flow Rate Research Articles

Electricity and hydrogen co-production via scramjet multi-expansion open cooling cycle coupled with a PEM electrolyzer

A scramjet multi-stage open cooling cycle for co-production of electricity and hydrogen is proposed here in which the fuel of the scramjet is used as coolant of the cooling cycle. Energy and exergy analysis of the devised system are conducted to evaluate the performance of the system and the effects of multi-expansion deliberation. In this integrated system, the waste heat of the scramjet cooling cycle drives the power sub-cycle in which a portion of the overall produced power supplies the required electricity of the proton exchange membrane (PEM) electrolyzer for hydrogen production. The results indicated that a four-stage open cooling cycle can be the best scenario in terms of providing more cooling capacity, electricity, and H2 production as well as a reasonable investment cost of its turbines. However, in the case when weight and size of the proposed cogeneration system are very important, a two-stage open cooling cycle can be appropriate. For the fuel mass flow rate of 0.4 kg/s and freestream condition of MaA=6, TA = 223 K and PA = 2.5 kPa, the cooling capacity, net electricity, and hydrogen production of the proposed system with four stages are computed 11.167 MW, 4.48 MW and 55.23 kg/h, respectively. On the other hand, the exergy results showed that PEM electrolyzer has the highest exergy destruction ratio by 70.66% among different components of the set-up. Moreover, the results of exergy analysis exhibited that employing the concept of multi-expansion outstandingly reduces the overall exergy destruction of the system. In this case, the energy and exergy efficiencies of the overall set-up (four stages) are computed 14.07% and 17.44%, respectively. The results of parametric evaluation demonstrated that increasing the back pressure of pump leads to more electricity and hydrogen production. But, increasing the mass flow rate of fuel hasn’t any tangible impact on energy and exergy efficiency.

Measurement and analysis of the in-cylinder process of a LNG engine under transient operations

Parameters reflecting the in-cylinder process in a turbocharged, LNG fuelled, spark ignited engine, such as the intake manifold pressure, air/fuel ratio (AFR), fuel mass flow-rate, as well as the dynamic in-cylinder pressure traces, are measured cycle-by-cycle for a series of transient operations via external air injection into the engine intake system. During the transient load step process, the engine experiences not only abrupt change of boost pressure and AFR, but also rapid engine load change. The changes in the in-cylinder combustion process during the transient operations, which were rarely revealed before, are illustrated with the rate of heat release (ROHR) characteristics cycle-by-cycle. The influences on the combustion characteristics under the transient operation conditions, of the operational parameters, such as AFR, air and fuel flow, boost pressure, etc. are examined and discussed. Existence of abnormal combustion such as late combustion, misfiring and severe variation of IMEP, etc. are pointed out. The possible causes of those abnormal combustion phenomena are also analyzed. The in-cylinder process detection method presented in this paper is universal and can be extended to other similar applications.

Experimental characterization of a solid oxide fuel cell coupled to a steam-driven micro anode off-gas recirculation fan

While the global fuel utilization of solid oxide fuel cells (SOFCs) is limited by the stack aging rate, the fuel excess is typically used in a burner, and thus limiting the system electrical efficiency. Further, natural-gas-fueled SOFCs require treated water for the steam reforming process, which increases operational cost.Here, we introduce a novel micro anode off-gas recirculation fan that is driven by a partial-admission (21%) and low-reaction (15%) steam turbine with a tip diameter of 15 mm. The 30 W turbine is propelled by pressurized steam, which is generated from the excess stack heat. The shaft runs on dynamic steam-lubricated bearings and rotates up to 175 krpm.For a global fuel utilization of 75% and a constant fuel mass flow rate, the electrical gross DC efficiency based on the lower heating value was improved from 52 % to 57 % with the anode off-gas recirculation, while the local fuel utilization decreased from 75% to 61%, which is expected to significantly increase stack lifetime. For a global fuel utilization of 85%, gross efficiencies of 66% in part load (4.5 kWe) and 61% in full load (6.3 kWe) were achieved with the anode off-gas recirculation. The results suggest that the steam-driven anode off-gas recirculation can achieve a neutral water consumption.

Transient system simulation for an aircraft engine using a data-driven model

In this paper, a simulation approach using a data-driven model to predict the performance of a gas turbine for aircraft engines during transient operations is proposed. The low bypass ratio and mixed-flow turbofan engine is considered in the simulation. The input parameters for the training of the data-driven model are fuel mass flow rate, altitude, flight Mach number, and the required power due to the moments of inertia of the rotating parts. The output parameters in the data-driven model are engine net thrust, low-pressure shaft rotating speed, pressure and temperature at each station, propulsion efficiency, efficiency of energy conversion and the overall efficiency. The data-driven model is trained using the data set obtained from a validated first principle model. In the simulation, using the data-driven model, the final engine performance is calculated using an iterative calculation for converging the power balance equation that considers the required power due to the moments of inertia at each time step. The transient performance simulation is tested during a throttle frequency sweep maneuver. In a comparison between the first principle model and the proposed simulation approach, the R-squared values of the output parameters are higher than 0.98, except for the efficiency of energy conversion and the overall efficiency, which register 0.9715 and 0.9183, respectively. It has been confirmed that the proposed simulation approach using the data-driven model can be applied to the transient simulation.

Effect of ambient pressure oscillation on the primary breakup of cylindrical liquid jet spray

The present simulation study investigates the effects of ambient pressure oscillation on cylindrical liquid jet sprays, using the volume of fluid method. The research is motivated by combustion instability in combustion engines, where strong harmonic pressure oscillation can damage internal structures. Oscillating pressure modulates not only the fuel mass flow rate but also the ambient gas density and liquid surface tension, and in liquid sprays, the ambient fluid density and surface tension can have substantial effects on spray breakup. In order to investigate the multiple property changes with ambient pressure oscillation, therefore, a new solver in OpenFOAM is developed. In the solver, liquid mass flow rate, ambient gas density, and liquid surface tension change simultaneously as a result of pressure oscillation. Simulations were conducted at a Reynolds number of 2000 and Weber number over 2000, conditions that are conducive to primary breakup in laminar flows. The simulations show that oscillations in ambient pressure significantly strengthen the surface instability of the liquid ligament, which depends on the surface tension–pressure coefficient, the mean pressure, and the amplitude of oscillation.

Identification of Air-Fuel Ratio for a High-Temperature and High-Speed Heat-Airflow Test System Based on Support Vector Machine

Air-fuel ratio is an important parameter in high-temperature and high-speed heat-airflow test system. If air-fuel ratio of the system is too low, the fuel cannot be fully burned, which will not only reduce the control performance of the gas temperature, but also increase the pollutant emissions of the combustor. In order to solve this problem, it is necessary to identify the air-fuel ratio of the system, get the prediction model of the air-fuel ratio, and adjust the fuel input according to the prediction value of the air-fuel ratio. In order to realize the accurate identification of the air-fuel ratio of the system, this paper briefly analyses the mathematical model of the air-fuel ratio in high-temperature and high-speed heat-airflow test system, and proposes an identification method of the air-fuel ratio based on support vector machine. On the basis of the experimental data, the air-fuel ratio of the system is identified by using different kernels, i.e. firstly, the experimental scheme is designed, and the fuel mass flow rate, air mass flow rate, gas temperature and actual air-fuel ratio of the system are collected under different experimental conditions; then, the collected data are divided into training datasets and test datasets, and the training datasets are trained by support vector machine to obtain identification model of the air-fuel ratio; finally, the identification model is validated with test datasets under different conditions, and the accuracy of the model is obtained. The identification results show that the support vector machine has good identification performance and can accurately approximate the actual dynamic process of the air-fuel ratio. The average absolute error of the identification model is less than 0.05, and the average relative error is less than 0.5% when the test datasets are smaller than the training datasets.

Analysis of Gas Turbine Operation before and after Major Maintenance

This paper presents an analysis of the gas turbine real process (with all losses included) before and after a major maintenance. The analysis of both gas turbine operating regimes is based on data measured during its exploitation. Contrary to authors’ expectations, the major maintenance process did not result either in any decrease in losses or increase in efficiencies for the majority of the gas turbine components. However, the major maintenance influenced positively the gas turbine combustion chambers (reduction in losses and increase in the combustion chambers efficiency). After the major maintenance, the overall process efficiency decreased from 43.796% to 41.319% due to a significant decrease in the air mass flow rate and to an increase in the fuel mass flow rate in combustion chambers. A decrease in the gas turbine produced cumulative and useful power after a major maintenance also increased the specific fuel consumption.

Evaluation of A Four Stroke Compression-Ignition Engine with Load (100N).

A loaded four stroke compression ignition (Nissan Primera model) engine mounted in a heat engine laboratory of Enugu State University of Science and Technology Enugu was used for the exercise. An absorption dynamometer was attached to the engine to measure torque. As the engine was running, the speed was recorded with a digital tachometer at a time frame of 20 seconds. A lot of tests were carried out to determine a number of parameters like specific fuel consumption, mechanical efficiency, fuel mass flow rate, indicated power, brake power, brake horse power, rate of fuel consumption at different gear ratios. The data so obtained were tabulated and relationship between various parameters plotted in graphs. Results show that: volume of diesel consumed increases with increasing engine speed, increases with increasing gear; mass flow rate of diesel increases with increasing brake power, increases with increasing gear; specific fuel consumption decreases with increasing engine speed ; specific fuel consumption also decreases with increasing brake power; indicated power increases as engine speed increases. Keywords : Diesel Engine, Absorption Dynamometer, Tachometer, Engine Torque, Brake Horse Power, DOI : 10.7176/JETP/9-8-04 Publication date: November 30 th 2019

Energy Efficiency Ratio (EER) of Novel Air Conditioning System on LPG Fuelled Vehicle: A Lab-Scale Investigation

Alternative fuels have become an effective solution to reduce the impact of road transport on the environment. On the other hand, the growing uses of air-conditioning (AC) have contributed to worsening the fuel economy of passenger vehicles. Liquid petroleum gas (LPG), if injected in the gaseous phase to power SI engines, may allow reducing the fuel consumption due to AC devices through the recovery of cooling energy from the fuel systems. This paper presents lab-scale tests of an air conditioning system prototype for LPG-fuelled vehicles. The prototype has been assembled using standard vehicle components to quantify the cooling energy recoverable from the LPG evaporation before the fuel is injected into the engine intake manifold. Temperature and humidity of the air exiting the LPG evaporator are measured for fuel mass flow rates typical of light-duty vehicles. The energy efficiency ratio (EER) of the prototype achieves 2.72 when cooling power equals 1.2 kW. Although the system tested needs improvements, the experimental data show that the cooling energy recovered by LPG evaporation can significantly reduce the power consumption of standard AC systems in passenger cars.

Engine Performance of a Gardener Compression Ignition Engine using Rapeseed Methyl Esther

This paper presents an experimental investigation on the influence of engine speed on the combustion characteristics of a Gardener compression ignition engine fueled with rapeseed methyl esther (RME). The engine has a maximum power of 14.4 kW and maximum speed of 1500 rpm. The experiment was carried out at speeds of 750 and 1250 rpm under loads of 4, 8, 12, 16 and 18 kg. Variations of cylinder pressure with crank angle degrees and cylinder volume have been examined. It was found that RME demonstrated short ignition delay primarily due to its high cetane number and leaner fuel properties (equivalence ratio (φ) = 0.22 at 4kg). An increase in thermal efficiency but decrease in volumetric efficiency was recorded due to increased brake loads. Variations in fuel mass flow rate, air mass flow rate, exhaust gas temperatures and equivalence ratio with respect to brake mean effective pressure at engine speeds of 750 and 1250 rpm were also demonstrated in this paper. Higher engine speed of 1250 rpm resulted in higher fuel and air mass flow rates, exhaust temperature, brake power and equivalent ratio but lower volumetric efficiency. Keywords— combustion characteristics, engine performance, engine speed, rapeseed methyl Esther

Testing and evaluation program of lab. scale hybrid propulsion system

The objective of the present paper is to prove the validity design and fully automatically operation of HPS, seeking to achieve its safety, low cost, and flexibility. In the stage of preliminary design, a coupling between experimental and theoretical work has been done, making use of available laboratory facilities and software packages (thermo-chemical calculation), to fully demonstrate all operating conditions. The HPS design includes the solid fuel grain configuration, essential operating parameters, oxidizer feed through control devices, measuring tools with calibration system, data recording and operating system. Commercial fuel materials as Polymethyl methacrylate (PMMA) and Polyethylene (PE) are used during experimental work to represent conventional generation fuel. Furthermore, new generation fuels as paraffin, beeswax, and paraffin with energetic additive metal (AL powder) are used. Gaseous oxygen is used as oxidizer. That may guide to design and fabricate high performance real rocket weapon or space propulsion system, targeting longer term storage and a propulsion system with available technology. The objective is extended to select appropriate ignition system (NiCr coil igniter) for laboratory firing of small-scale engine. One of the main problems (price, safety, available technology) of propulsion system today has been tackled. To that end, analysis has been established, to investigate the regression rate, solid fuel mass flow rate and combustion efficiency for each fuel grain group types.

Black-box modelling of gas turbine engine’s electrohydraulic fuel metering system.

The fuel and air flow rates are the main parameters affecting the gas turbine engine performance. The burned fuel in the combustor is the main source of heat energy. The fuel metering system (FMS) provide these engines with precise fuel mass flow rates required for regulation process. One of the most important and challenging concerns of engine design and control is, driving a valid model for the FMS. Physics-based models require well identification of the electrical and hydraulic system parameters. Measuring these parameters for the system under study, like the internal dimensions of these system components is very hard because of the system complicity and integrity. In this case it is preferred to treat the system as a black box. In this paper a transfer function model for an electrohydraulic FMS has been estimated and validated using MATLAB system identification toolbox (SIT). FMS closed loop measurements have been done for data set preparation process. Linear Variable Differential Transformer (LVDT) integrated in this system has been used for measuring the metering valve displacement which is proportionally represents the output mass flow rate. Linear variable differential transformer (LVDT) signal conditioning circuit has been designed and implemented to provide DC output voltage, proportional to the system output volume flow rate. Another conditioning circuit has been designed for output current amplification process required for electrical solenoid driving. The driven transfer function model has been validated using a different measured data set to insure a good representation of the physical system. Results show that the obtained model follows the real system with good accuracy and demonstrate the effectiveness of the transfer function modelling for the FMS.

Beeswax Material: Non-Conventional Solid Fuel for Hybrid Rocket Motors

Traditional solid fuel for Hybrid Rocket Motor (HRM) is characterized as a low regression rate, aiming to develop a new generation of solid fuel material that combines at the same time good ballistic properties, easy manufacture, safe exhaust emission and low cost. Beeswax as bio-derived hydrocarbon fuel has been evaluated to be used as solid fuel in HRM. Firing tests are carried out at the average pre-chamber pressure of 2.90 bar, the oxidizer mass flow rate of 9.34 g/s and the regression rate of 1.5 mm/s at combustion efficiency reaches 60.3 %. Beeswax as pure solid fuel grain at 7 mm active channel port with 100 mm length is tested with gaseous oxygen (gO2) as oxidizer and it showed a regression rate at least three times as high as traditional hybrid propellant, such as Polymethyl methacrylate (PMMA) and Polyethylene (PE)/gO2. This provides a promise for high performance parameters with a special regression rate to overcome the main drawbacks of traditional hybrid propellant. Experimental evaluation parameters (regression rate, fuel mass flow rate and combustion efficiency) are carried out for beeswax/gO2. Combustion shows fairly successful results for lab scale testing but it needs further enhancement, especially in combustion efficiency and theoretical studies for combustion efficiency.

Diesel fuel combustion in a direct-flow evaporative burner with superheated steam supply

A method of liquid hydrocarbon combustion in a new evaporative burner with a controlled forced supply of superheated steam jet into the reaction zone was experimentally studied in this paper using diesel fuel. For the first time, dependences of the flame temperature and thermal and environmental characteristics on the steam flow rate and overheating were obtained. The boundaries of characteristic combustion regimes were determined. During fuel combustion in a superheated steam jet, the concentrations of nitrogen oxide and carbon monoxide in the combustion products are significantly lower than the maximum permissible concentrations established for this type of burner device, according to EN 267: 0–5 ppm for CO and 25–50 ppm for NOx. The relative steam mass flow rate, in contrast to the steam temperature, substantially influences the main characteristics of the combustion process. Maximum heat release 45 MJ/kg is achieved in a system in which the steam mass flow rate equals half of the fuel mass flow rate. The new combustion method ensures high-energy efficiency and environmental safety and may be used in the development of technologies for the disposal of nonstandard liquid hydrocarbon fuels and industrial wastes with simultaneous heat energy production.

Studi Kemungkinan Pemakaian Sekam dan Jerami Padi sebagai Bahan Bakar Briket untuk Ketel Uap di RSUP dr. Wahidin Sudirohusodo Makassar

This study aims to: (1) make briquettes from rice husk and straw with some mixture proportions, (2) determine the heating value (HHV) and the compressive strength of the produced briquettes (3) determine the physical properties of the produced briquettes through the proximate analysis and determine the best briquettes mixture, and (4) know the possibility of using rice husk and straw as briquette fuel for steam boilers. The produced briquettes contained 85% of rice husk charcoal and straw, and adhesive subtance consisting of clay (10%) and strach (5%). The briquettes were made with five mixture proportions with an average mass ratio of 260 gramsduce briquettes briquette type E as the best. The examination of heating value reveals that the higher the percentage of staw in the mixture, the lower the briquette heating value will be; while the testing of compressive strength reveals that the higher the percentage of straw in the mixture, the higher the briquette compressive strength will be. Based on the proximate analysis, it is found that generally the produced briquettes have fulfilled the briquette standard quality. The results of calculations analysis reveal that there is a possibility to use briquettes made of rice husks and straw as steam boilers the ratio between the fuel mass flow rate and vapor mass flow rate is 0.231.

Numerical investigation of the liquid-fueled pulse detonation engine for different operating conditions

In this study, an intensive simulation platform is developed and implemented to simulate the three stages in the operational cycle of the liquid-fueled pulse detonation engine. The three stages encompass the liquid fuel injection and evaporation process, deflagration-to-detonation transition process, and detonation propagation process. The Lagrangian–Eulerian approaches are employed to model the discrete liquid fuel droplets and the continuous vapor phase, respectively. The breakup and evaporation of liquid droplets are modeled using sub-models, while the interactions between the liquid droplets and the vapor phase are expressed through the two-way interaction models. The Jet-A liquid fuel is injected into the detonation chamber as the fuel for the engine, while the air flow is used as the oxidizer. A reduced chemical kinetic model of fuel/air is used to model the combustion process. The simulation platform is systematically validated against the experimental data for every stage of the operating cycle. To study the influence of the inlet and operating conditions, the numerical simulations are performed for three different operating conditions, which are the change in inlet air temperature, the change in inlet air flow velocity, and the change in liquid fuel mass flow rate. The obtained results indicate that the mass fraction of pre-vaporization of fuel plays an important role in the successful DDT process and/or detonation onset. The deflagration can successfully transit to detonation for both the cases of complete and incomplete vaporization of the liquid droplets inside the detonation chamber. The deflagration cannot successfully transit to detonation for the case of too lean or too rich fuel vapor in the mixture. The calculated burning temperature and Chapman–Jouguet (C–J) detonation velocity are slightly lower in the cases of the incomplete vaporization when compared to the complete vaporization cases. In addition, our numerical results show that the burning process occurs in two stages in the incomplete vaporization case: The first burning stage plays a main role in the successful DDT process, while the second burning stage only plays the role of augmentation.

Thermodynamic modeling and analysis of a novel heat recovery system in a natural gas city gate station

In the present study, five configurations of integrated system are introduced and comprehensive thermodynamic modeling and analysis for different arrangements are carried out. An organic Rankine flash cycle (ORFC) and a thermoelectric generator (TEG) are integrated with a real city gate station (CGS) to recover the thermal energy of exhaust gas at 400 °C in an indirect water bath heater (IWBH). The new aspect of the present research is proposal the novel arrangements of the TEG modules, ORFC and IWBH to improve the thermal performance of the CGS integrated system.Energy and exergy analyses employed to evaluate different arrangements of integrated systems.Comparative analysis of different suggested systems revealed that integrated system including IWBH, ORFC and TEG modules with placing the TEG modules after ORFC (Case V) shows better performance. Due to the better performance, Case V is considered for more studies. Under the given condition for the selected case, in a complete year, results indicate that the maximum and minimum values of electrical output power for TEG modules is 132 W and 100 W and for ORFC is 11.5 kW and 2.1 kW. Also, the parametric study of the Case V inferred that with increasing the amount of excess air form 50%–200%, the fuel mass flow rate increased by 35.6% which ultimately leads to a reduction in thermal efficiency of the system. The results suggests that proper arrangement of TEG modules and ORFC in the IWBH can improve the total thermal efficiency as well as the total electrical output power. Analyses of different proposed arrangements, also indicates that with the use ORFC and TEG modules in the worst and best cases 2.284 kW and 5.904 kW electrical energy can be recovered from the IWBH in the CGS.

Mathematical model of a supercritical power boiler for simulating rapid changes in boiler thermal loading

This paper presents a new online-ready mathematical model of a supercritical power boiler, which enables comprehensive analysis of the boiler dynamics. The model allows generating modified sliding curves for a power unit that is currently under construction in one of a Polish power plant. The modified sliding curves illustrate the transients of the steam at the turbine inlet, which varies depending on the power unit load. The developed model allows analysing the boiler operation during start-up from cold, warm, and hot states. Moreover, the model allows simulating the boiler operation when the power unit output increases by 7.5% and 5% in a specified period.To satisfy the requirement of increasing the power unit load by 5% in a set period, the live steam mass flow rate must be increased at the boiler outlet. For this purpose, the live steam pressure at the turbine inlet is reduced, and the fuel mass flow rate is increased simultaneously. This results in an increase in the live steam mass flow rate at the boiler outlet. The total increase in the live steam mass flow rate can be determined using the developed model. After the pressure decrease process is stopped, the required level in the steam mass flow rate at the boiler outlet should be achieved only by firing more fuel. The only approach to obtain the appropriate values of the target decrease in the pressure at a set load, in the range of the power unit loads from 40% to 80%, is to develop a mathematical model of the entire boiler and perform the simulations.All the simulations are performed using an in-house developed computer program.

Performance evaluation of an integrated proton exchange membrane fuel cell system with ejector absorption refrigeration cycle

Absorption chiller systems are advantageous to vapor compression cooling systems due to capability of utilizing low-grade heat sources such as waste heat from industries, renewable energies, and generated heat by fuel cell. The main issue in absorption cooling system is the low cycle coefficient of performance (COP) that can be addressed by integrated ejector-absorption cooling systems. In this study, an integrated system of proton exchange membrane (PEM) fuel cell that thermally drives an ejector-absorption refrigeration cycle is proposed. The effects of generator temperature, condenser pressure, evaporator pressure, and inlet fuel mass flow rate to the fuel cell on the ejector entrainment ratio (ϕ) and COP are evaluated. Moreover, the performance of the integrated system is evaluated at different geometrical and operating conditions of PEM fuel cell. The results reveal that the ϕ and COP parameters increase up to 18.51% and 48% by increasing the generator temperature from 70 °C to 100 °C, respectively. At higher inlet mass flow rate of fuel to the reformer, the cooling capacity and the system COP improve. Furthermore, the maximum value of ϕ and COP are 0.39 and 0.77, respectively, at the best operating condition of the PEM fuel cell, i.e. the current density of 0.75 A/cm2. It is also concluded that the system overall energy efficiency at temperature of 80 °C and the current density of 0.5, 0.6, 0.75, and 0.85 A/cm2 are 43%, 39%, 35%, 32%, and 37%, respectively. Moreover, the COP of absorption chiller with ejector at the operating pressure of 1 bar and the temperature of 80 °C for PEM fuel cell is 6.7% higher than conventional absorption chiller.

Simulation of rapid increase in the steam mass flow rate at a supercritical power boiler outlet

The paper presents selected results of simulations of a rapid increase in the supercritical power boiler thermal load. The simulations concerned the possibility of obtaining the required increase in the live steam mass flow rate at the boiler outlet in a set period. This condition must be met to achieve the required increase in the power unit load, of the order of a few dozen MW in a few dozen seconds. For this purpose, it is necessary to decrease the boiler pressure and increase the fired fuel mass flow rate at the same time. The pressure reduction is carried out by opening, at a constant rate, the control valves installed on the pipeline at the turbine inlet. Assuming that the rate is known, the unknown parameters are the values of the target pressure reduction and the time of the pressure decrease process duration. The values vary depending on the power unit initial load. After the pressure decrease process is stopped, the required increase in the power unit load (the increase in the live steam mass flow rate) should be maintained only by firing more fuel. The required values of the target reduction in pressure within a specific range of the power unit load can only be determined by developing a precise mathematical model of the entire boiler and performing simulation computations. The obtained results are of fundamental practical importance because they are used by the boiler manufacturer to generate the power unit modified sliding curves. The results presented in the paper relate to a supercritical power unit now being constructed in one of the Polish power plants. An in-house mathematical model was developed for the power unit boiler. The model comprises all heating surfaces of the boiler and enables simulation of the boiler operation in conditions of rapid changes in loads.