Exhaust Heat Loss Research Articles

A novel swiss-roll counterflow micro-combustor: Experimental investigation of methane-oxygen flame behavior over time

This study introduces a novel Swiss-roll micro-combustor design that employs a non-premixed counterflow flame for efficient and stable micro-combustion. This design addresses practical system challenges by (1) stabilizing the flame, (2) enhancing heat recovery and gas preheating, (3) aligning gas momentum with the exhaust, and (4) minimizing disruptive fluid motion within the channels. This research investigates the dynamic behavior and combustion characteristics of a methane-oxygen flame within the combustor across a range of equivalence ratios (1.50–3.38). A synergistic approach combining flame dynamics analysis, spectroscopy, and RGB image processing explores the interplay between flame temperature, strain rate, and equivalence ratio. The results demonstrate the effectiveness of the RGB method as a cost-efficient tool for predicting variations in C2∗ and CH∗ radicals and light-intensity radiations. While flame thickness and length exhibit complex dependencies on the fuel-to-oxygen ratio and wall temperature, specific radical emissions vary dynamically with the equivalence ratio. Notably, equivalence ratios of 1.94 and 2.26 exhibit minimal temporal variations in flame properties, suggesting optimal stability and predictability for practical applications. The investigated flame is classified as a “cool flame,” and efficiency declines with richer mixtures due to increased exhaust heat loss and incomplete combustion. This work paves the way for further micro-combustor design optimization and unlocks the potential of non-premixed counterflow flames in diverse micro-scale applications.

Effects of dimethyl ether blending on H2-fueled combustion characteristics and thermal improvement in fuel-lean condition

Micro-combustors play a pivotal role in micro powering system due to the potential for high energy density. However, addressing challenges such as incomplete combustion and high heat dissipation losses are essential for optimizing the working performance. So, the blended DME is proposed to micro-combustion, which acts as a promising oxygenated fuel with significant attention due to its higher reactivity, lower pollutant emissions, and carbon–neutral properties. However, the lack of dynamic models applicable to H2/DME fueled combustion in micro condition, so an optimized mechanism for blended H2/DME combustion is developed and validated. The results demonstrate that a reduced mechanism comprising 29 species and 106 reactions (M29-106*) can be commendably employed in micro H2/DME/air combustion simulation, according to the sensitivity analysis and reaction modification. Besides, investigation is conducted to explore micro-combustion characteristics of H2/DME/Air. The result shows that burning process and heat transfer are notably influenced by DME addition, leading to shifts in flame positions and adjustments in combustion reaction rates. So, DME addition enhances energy efficiency and modifies flame location through fluid field optimization and reduced heat loss. The thermal performance of the combustor is significantly improved with DME blending, resulting in higher radiative power and radiation efficiency. However, the choice of DME blending ratio must be carefully considered, as high blending ratios may compromise flame stability and lead to increased exhaust heat losses under fuel-lean conditions. Specifically, burning with 30 % DME addition achieves a radiative power of 20.24 W and a radiative efficiency of 40.57 % at the same chemical energy Ec = 49.9 W, which is 5.57 W and 11.17 % higher than that of pure H2-fueled combustion, respectively. These findings offer valuable insights for the design and optimization of micro-combustors, where compact and efficient power sources are required.

Effects of methanol direct injection and high compression ratio on improving the performances of a spark-ignition passenger car engine

The high octane number and high latent heat of vaporization of methanol are beneficial to suppress knock and consequently increase compression ratio (CR) of spark ignition engines, and thus improve the thermal efficiency. Few preious research on methanol engine combuston and performances have been conducted based on spark-ignition passenger car engines with a CR greater than 14. In this study, a 1.5-liter spark ignition passenger car engine with miller cycle was used to explore the potentials of high CR and methanol direct injection (MDI) on improving engine performances. First, the engine was tested under stoichiometric combustion using methanol and gasoline at BMEPs of 1.1 MPa and 1.5 MPa with CR11.5, CR13.8, and CR15.3. Then, the performances of the CR11.5 case with gasoline and the CR15.3 case with methanol were compared under lean burn combustion. The results show that for gasoline, increasing CR from 11.5 to 15.3 results in decreased fuel economy under stoichiometric combustion, whereas the exact opposite tendency is shown for methanol. Integrating a high CR of 15.3 and MDI improves brake thermal efficiency (BTE) to 43.3 % at an excess air/fuel ratio (λ) of 1.0, when compared with 37.4 % of gasoline at CR11.5. Applying lean burn can further improve the BTE of methanol at CR15.3 to 44.9 %. The main causes of the improvement of BTE by high CR and MDI are the reduced exhaust heat loss resulted from earlier combustion phasing. However, high CR and MDI also extend combustion durations at all specified λs, and emit more THC and CO emissions than low CR with gasoline at high λs because of higher surface/volume ratio and flame quenching. The extended combustion duration and the incomplete combustion are the main barriers to greater BTE for MDI sprak ignition engine with high CR.

Thermoelectric Generation From Exhaust Heat in Electrified Natural Gas Trucks: Modeling and Analysis of an Integrated Engine System Performance Improvement

AbstractUsing thermoelectric generators (TEG) to reduce exhaust heat loss from internal combustion engines can improve emissions and the fuel economy of conventional and electrified vehicles. However, TEG potentials have not been investigated in hybridized, compressed natural gas (CNG), twin-turbocharged, and spark-ignited (SI) engines. This work demonstrates TEG's effectiveness in boosting a hybridized 3.0 L CNG engine using model-based development. TEG experiments are performed to measure thermal performances under different inlet gas conditions for model validations. Simplified user-defined functions of flow friction and heat transfer coefficients are used to calibrate the model. A fast-calibration model can reproduce measured heat transfer, pressure drop, and thermal performances. The engine performances are validated against measured 35 steady-state conditions from the production engine used in light-duty CNG trucks under the JE05 drive cycle. Next, the model is connected to the turbocharging system downstream of the well-calibrated four-cylinder SI engine model. Under the peak performance condition (peak brake thermal efficiency BTE at 2400 RPM and 102 kW load), the results show that the engine BTE is improved by 0.56% using a 7 × 9 TEG module arrangement (three-sheet TEG with 1.5× A4 size). A 9 × 10 arrangement can enhance the BTE to 0.8%. Effective electrical power is generated up to 1.168 kW from the TEG, depending on the JE05 operating regions, without significant brake power loss.

Mathematical Model of Hot Water Boiler and its Experimental Validation

Low efficiency of isolated heat supply systems based on coal-fired hot water boilers requires the search of feasible control systems reducing incomplete combustion and exhaust heat losses. The paper considers a mathematical model enabling to calculate burned coal weight and boiler efficiency by a measurement set of various parameters. The proposed model is successfully validated on an experimental unit simulating a heat supply system and can be used to develop various control systems for hot water boilers, including adaptive ones.

Exergy and energy analysis during cold-start and warm-up engine operation

Cold-start is an inevitable part of the daily driving operation for most vehicles. Given that exergy analysis can evaluate the sources of losses qualitatively and quantitatively using the first and second laws of thermodynamics, this study investigated the impact of engine temperature on energy and exergy parameters during engine warm-up. Using a turbocharged Cummins engine, the performance and emissions data were measured, and energy and exergy parameters were formulated from the experimental data. Engine warm-up period was divided into seven phases, including official hot-start and cold-start, and some phases which are not considered as cold-start or hot-start by regulations. This study evaluated different parameters related to energy analysis (brake power, friction mean effective pressure [FMEP], brake specific fuel consumption [BSFC] and brake thermal efficiency [BTE]), exergy analysis (fuel input exergy, exhaust heat loss, exergy destruction and exergetic efficiency) and their correlations. Results showed that as the engine warmed up, the fuel exergy, exhaust heat losses, and exergy destruction decreased by 2.3, 34.1 and 34.1%, respectively; while, the exhaust exergy loss increased by 43.5%. The FMEP and BSFC decreased by 56.7% and 14.9% as the engine warmed up, while BTE and the exergetic efficiency increased by 5.6% and 5.3%, respectively.

Experimental exergy analyses in aDIdiesel engine fuelled with a mixture of diesel fuel andTiO2nano‐particle

AbstractIn this study, the operation of a four‐cylinder, four‐stroke DI diesel engine powered by fuels created by blending diesel and TiO2nanoparticles was evaluated based on energy and exergy analyses. Within the study's scope, it is possible to see the engine's performance, combustion, emission, and heat transfer distribution at various engine speeds. The engine was tested by operating it with diesel and fuel blends, diesel‐2.5 ppm TiO2. According to obtained results, it was found that by adding 2.5 ppm TiO2to diesel fuel, energy and exergy efficiency increased by 4.1% and 3%. Engine power and shaft exergy improved by 3.4%, and diesel‐2.5 ppm TiO2blends decreased irreversibility by 3.8%. Diesel‐2.5 ppm TiO2blended fuel decreases the exhaust loss exergy and exhaust heat losses by 2.5% and 1.4% and also uncounted heat losses reduced by 5.7% compared with baseline diesel. Moreover, the exergy transfer with cooling water increased by 10.5% compared with baseline diesel fuel. The brake specific fuel consumption was 3% lower for diesel and 2.5 ppm TiO2nanoparticle blended fuels. The engine fueled with blended fuel revealed mitigation in the UHC, CO, and Soot emissions than those of diesel fuel. NOx emission exhibited increasing trends with the blended fuel. It is concluded that diesel blend with the addition of TiO2nanoparticles exhibits better engine performance and reduced emissions compared to diesel fuel.

Dual-radiation-chamber coordinated overall energy efficiency scheduling solution for ethylene cracking process regarding multi-parameter setting and multi-flow allocation

This work proposes a novel energy efficiency scheduling solution for cracking process, which achieves energy efficiency improvement comprehensively and scientifically. The proposed solution reflects several significant features of process operation, for example, the impact of COT, COP, and dilution ratio on product output and energy utilization, the influence of SHS recycle energy and exhaust gas energy loss on fuel and DS consumption. Also, DRC independent parameter setting and asynchronous batch processing have also been taken into account with scheduling of cracking furnace groups. Ethylene cracking process is the core production process in ethylene industry, and is paid more attention to reduce high energy consumption. Because of the interdependent relationships between multi-flow allocation and multi-parameter setting in cracking process, it is difficult to find the overall energy efficiency scheduling for the purpose of saving energy. The traditional scheduling solutions with optimal economic benefit are not applicable for energy efficiency scheduling issue due to the neglecting of recycle and lost energy, as well as critical operation parameters as coil outlet pressure (COP) and dilution ratio. In addition, the scheduling solutions mostly regard each cracking furnace as an elementary unit, regardless of the coordinated operation of internal dual radiation chambers (DRC). Therefore, to improve energy utilization and production operation, a novel energy efficiency scheduling solution for ethylene cracking process is proposed in this paper. Specifically, steam heat recycle and exhaust heat loss are considered in cracking process based on 6 types of extreme learning machine (ELM) based cracking models incorporating DRC operation and three operation parameters as coil outlet temperature (COT), COP, and dilution ratio according to semi-mechanism analysis. Then to provide long-term decision-making basis for energy efficiency scheduling, overall energy efficiency indexes, including overall output per unit net energy input (OONE), output-input ratio per unit net energy input (ORNE), exhaust gas heat loss ratio (EGHL), are designed based on input–output analysis in terms of material and energy flows. Finally, a multi-objective evolutionary algorithm based on decomposition (MOEA/D) is employed to solve the formulated multi-objective mixed-integer nonlinear programming (MOMINLP) model. The validities of the proposed scheduling solution are illustrated through a case study. The scheduling results demonstrate that an optimal balance between multi-flow allocation, multi-parameter setting, and DRC coordinated operation is reached, which achieves 3.37% and 2.63% decreases in net energy input for same product output and conversion ratio, as well as the 1.56% decrease in energy loss ratio.

Influence of flue gas recirculation on the performance of incinerator-waste heat boiler and NOx emission in a 500 t/d waste-to-energy plant

The flue gas composition and the flue gas temperature at outlet of the economizer were tested, and the influence of flue gas recirculation (FGR) on the efficiency of the incinerator-waste heat boiler and NOx emission in a waste incineration power plant with a waste disposal capacity of 500 t/d was explored experimentally. The results indicate that the largest proportion of the total heat loss is the exhaust heat loss under different loads, and the next is the heat loss of slag. Within the test range, the efficiency of the incinerator-waste heat boiler increases from 80.26% to 80.42% as the ratio of the recirculating flue gas increases from 0 to 16.43%. The oxygen content in the flue gas and FGR have significant influence on NOx emissions. The NOx concentration at outlet of the economizer increases from 209.54 mg/m3 to 307.30 mg/m3, that is an increase of 46.65%, when the oxygen content at outlet of the economizer increases from 4.52% to 8.00%. Compared with the shutdown of FGR system, the NOx concentration at outlet of the economizer decreases from 209.54 mg/m3 to 126.15 mg/m3 when the FGR valve is fully opened. The results have important reference significance for the design of incinerator-waste heat boiler and the optimal operation of power plant.

Online simplified model and experimental comparison of CFB boiler thermal efficiency

In recent years, circulating fluidized bed boiler (CFB) combustion technology, which is used as a purification technology in coal combustion, has been widely studied. Some studies have conducted simplified investigations into calculating the standard boiler thermal efficiency. However, these studies are mainly aimed at simplified calculations of the boiler’s heat balance and data correction, and an online prediction model based on the core influential parameters have not been developed.To solve this problem, this study first calculates the boiler heat balance and thermal efficiency calculation to analyze thermal efficiency calculation factors. The exhaust heat loss q2 and the incomplete combustion heat loss of gas q3 decrease as the slag carbon content increases. For every 1% increase in the slag carbon content, the thermal efficiency is reduced by 1.95%; for every 5 °C increase in the exhaust gas temperature, the thermal efficiency is reduced by 0.26%.Then a simplified boiler thermal efficiency model, based on the slag carbon content and exhaust gas temperature determined to be the core parameters, is derived and compared with the measured results. The functional relationship is derived as follows: η=98.012–0.053tpy-1.944Clz (tpy < 200 °C, Clz < 2%).

Turbine and exhaust ports thermal insulation impact on the engine efficiency and aftertreatment inlet temperature

Worldwide emission regulations are driven the efforts of the automotive industry to meet challenging targets concerning pollution reduction. Nowadays, advances in exhaust aftertreatment systems are primarily required to achieve regulation requirements within the whole engine operating range. Nevertheless, flow parameters, such as the exhaust gas temperature, must be also addressed. This makes engine calibration a fundamental step, but also leads to reconsider the passive design of the exhaust line as a way to improve the engine efficiency. Under this context, a study has been conducted to explore the benefits of heat losses limitation looking for aftertreatment inlet temperature increase at the same time fuel economy is improved. To do so, a baseline diesel engine has been modeled using a gas dynamic software taking special care of the heat transfer processes in the exhaust. The investigation covers the definition of different strategies for exhaust ports and turbine thermal insulation, which are evaluated in a representative range of steady-state operating conditions. As a first step, the theoretical limits and representative technology solutions are considered for each exhaust region. Then, a combination of the most promising strategies has been computed to provide a comprehensive database and analysis of the potential of passive exhaust heat losses control.

Application of Heat Pipe Technology in Thermal Power Plant

As is known to all, China’s main power plant to pulverized coal furnace is given priority to, all the losses from the burning of coal in boiler, exhaust loss is a main power plant boiler heat loss, exhaust smoke temperature is higher, the greater the exhaust heat loss of exhaust temperature data indicated that every 15 ∼ 20 °C, exhaust heat loss will be increased by 1%, corresponding to a 2% increase in coal consumption. When the air temperature of exhaust smoke temperature is higher than in boiler, part of heat is produced without being used, which affect the safety of boiler efficiency and operation efficiency, at the same time can also cause serious pollution to the environment. Therefore, it is of great significance to reduce the exhaust temperature effectively.

Design of Heat Exchanger for Waste Heat Recovery from Exhaust Gas of Diesel Engine

The Diesel Generating set (DG Set) which uses diesel engine is gaining popularity in rural areas as it produces electricity for irrigation and agricultural purposes. But there are various losses associated with diesel engine which tend to reduce its efficiency and performance. Among these exhaust heat loss is major loss which contribute almost 33-36% and leads to the waste of heat which could be recovered and a considerable amount of primary fuel could be saved. The literature survey reviews that exhaust gases from diesel engine having heat potential that can be recovered. In the present paper attempt have been made recovering of waste heat energy of exhaust gas of diesel engine by placing specially designed heat exchanger just near the inlet and outlet duct of the engine so that energy from the exhaust can be used for preheating the air passed to the engine. A simple counter flow shell and tube type heat exchanger was designed and fabricated based on the output obtained from initial design. The experiments were conducted with and without out heat exchanger on vertical, single cylinder, 5 HP, cold start, water cooled, four stroke diesel engine working on high speed diesel oil. The diesel engine with incorporation of heat exchanger shows improved performance of engine and also shown reduction in smoke level.

Influences of Gasoline Fuels on Waste Heat Recovery Potentiality of a Spark Ignition Engine

Objectives: In this study, evaluation of the potential of energy recovery in spark ignition engine using RON 95 gasoline fuels. Methods: The engine has been operated at a single engine speeds of 3500 RPM with 50% of Wide Throttle Open (WTO). The potential of energy recovery was measured by means of engine effective power, Water Heat Losses (WHL) and Exhaust Heat Losses (EHL). Findings: Comparative analysis of the experimental results showed an improvement of 1.16%, 2.12% and 3.08% in EHL at 75°C, 50°C and 25°C, respectively, by taking 120°C as the reference temperature of EHL. The results of the contour plot showed that a trade-off between the WHL and EHL. Conclusion: Higher proportions of energy losses can be utilised by considering both WHL and EHL.

Energy Balance Analysis on a Preheating Catalytic Oxidation Device of Coal Mine Ventilation Air Methane

Energy balance analysis was carried out during the operation process of a preheating catalytic oxidation device of coal mine ventilation air methane. The effects of space velocity, inlet gas temperature and methane volume concentration on each energy balance term were studied. The experimental results show that: the exothermic oxidation power and the surface heat dissipation power loss rise with the increase of methane volume concentration and the oxidation bed inlet temperature, and yet fall when space velocity achieves a high enough value; the exhaust heat power loss is enhanced significantly with the growth of the inlet temperature and space velocity, but the change of methane volume concentration has very little influence on the exhaust heat loss power; the fraction of the exhaust heat loss descends significantly with the increase of methane volume concentration and inlet temperature, and yet rises obviously with the improvement of space velocity. The above results provide a theoretical guidance on the stable self-heating maintenance operation of the preheating catalytic oxidation device.

Assessment of total efficiency in adiabatic engines

The paper presents influence of ceramic coating in all surfaces of the combustion chamber of SI four-stroke engine on working parameters mainly on heat balance and total efficiency. Three cases of engine were considered: standard without ceramic coating, fully adiabatic combustion chamber and engine with different thickness of ceramic coating. Consideration of adiabatic or semi-adiabatic engine was connected with mathematical modelling of heat transfer from the cylinder gas to the cooling medium. This model takes into account changeable convection coefficient based on the experimental formulas of Woschni, heat conductivity of multi-layer walls and also small effect of radiation in SI engines. The simulation model was elaborated with full heat transfer to the cooling medium and unsteady gas flow in the engine intake and exhaust systems. The computer program taking into account 0D model of engine processes in the cylinder and 1D model of gas flow was elaborated for determination of many basic engine thermodynamic parameters for Suzuki DR-Z400S 400 cc SI engine. The paper presents calculation results of influence of the ceramic coating thickness on indicated pressure, specific fuel consumption, cooling and exhaust heat losses. Next it were presented comparisons of effective power, heat losses in the cooling and exhaust systems, total efficiency in function of engine rotational speed and also comparison of temperature inside the cylinder for standard, semi-adiabatic and full adiabatic engine. On the basis of the achieved results it was found higher total efficiency of adiabatic engines at 2500 rpm from 27% for standard engine to 37% for full adiabatic engine.

Tunnel Dryer and Pneumatic Dryer Performance Evaluation to Improve Small‐Scale Cassava Processing in Tanzania

AbstractIn sub‐Saharan Africa, cassava is grown by smallholder farmers and is the principal source of calories for the local population. However, the short shelf life of cassava associated with poor infrastructure in the region results in significant postharvest losses. The expansion of small‐scale cassava processing could reduce these losses, but the availability of drying equipment suitable for use in such operations is limited. The objective of this research was to contribute to the development of cassava dryers suitable for use by smallholder farmers. A tunnel dryer and a pneumatic dryer being operated in Tanzania were evaluated using mass and energy balance analysis. It was found that the energy efficiency of the tunnel dryer was 29% and of the pneumatic dryer 46%. For the tunnel dryer, most of the heat losses were through unsaturated exhaust air, while for the pneumatic dryer, most losses were through radiation and convection.Practical ApplicationsIn this study, a tunnel dryer and a pneumatic dryer suitable for use by smallholder farmers were evaluated during processing centers' usual cassava drying operations. The sources and extent of heat losses were identified, and then guidelines developed on how to reduce such losses. For both dryer types, improvements to the thermal insulation used could reduce heat losses to the ambient. For the tunnel dryer, decreasing the air mass flow rate by 57% would help to minimize exhaust heat losses without producing condensation inside the unit. For the pneumatic dryer, air mass flow rate could be reduced by 9%, improving energy performance without having a negative impact on the pneumatic conveying of the product. Those two modifications would be easy to implement and represent a significant contribution to the development of small‐scale cassava drying technology.

Thermal Balancing of a Multi-Cylinder Diesel Engine Operating on Diesel, B5 and Palm Biodiesel Blends

Energy crisis and global warming are the two most important issues that threaten the peaceful existence of the human species. More dependency on alternative fuels and energy loss minimization can be an effective solution to this affair. In this regard, thermal balance study of an internal combustion (IC) engine using different biodiesels is worthy of investigation. This manuscript provides an in-depth analysis of the engine heat losses in different subsystems of the engine. Finally, thermal balancing of the engine has been done by showing all energy flows in and out of the engine. The investigation was conducted in a four cylinder diesel engine fuelled with pure diesel, B5 (5% Palm biodiesel + 95% Diesel), 10% (PB10) and 20% (PB20) palm biodiesel blends at full load and in the speed range 1000 to 4000 RPM. The water heat loss and lubricating oil heat loss increased whereas the engine brake power, exhaust heat loss and unaccounted heat loss decreased with the increase of biodiesel percentage in the blends.

Research on the Utilization of Exhaust Gas Heat for Boilers

The exhaust heat loss of the power plant boiler can account for more half of the boiler heat loss, exhaust gas temperature is 110~160 °Ccommonly, so the exhaust gas heat can be used to reduce the coal consumption, raise the economic benefits. Before and after the desulfurization tower of a 350 MW unit, there installs two plate heat exchangers, heating condensation water respectively, which can improve the thermal efficiency. With two heat exchangers working under the design conditions, a test was carried out based on a 350 WM unit simulation system in order to test the influence of system for unit operation characteristics. Referring to the data, the investment of the heat exchanger can achieve 2.68 g/kWh coal saving during the non-heating period and 0.2531 g/kWh during the heating period.

Load expansion of naphtha multiple premixed compression ignition (MPCI) and comparison with partially premixed compression ignition (PPCI) and conventional diesel combustion (CDC)

In previous studies, multiple premixed compression ignition (MPCI) has been proposed as a novel combustion concept in gasoline compression ignition engines which has great potential to achieve high thermal efficiency and low emissions simultaneously. MPCI mode was realized by a sequence of “spray–combustion–spray–combustion” around the compression top dead center (TDC). This study is aimed for the high load expansion of naphtha MPCI. In addition, the study investigated advantages and disadvantages of MPCI compared with partially premixed compression ignition (PPCI) and conventional diesel combustion (CDC). Engine operating range successfully reached indicated mean effective pressure (IMEP) of 1.4MPa with high thermal efficiency, low emissions and acceptable combustion noise by the optimization of the injection parameters and the intake management.For MPCI, earlier combustion phasing was possible even at the high load operation compared with PPCI and CDC. This was attributed to the separated heat release characteristics and pressure rise rate process. The divided pressure rise rate process caused considerably low maximum pressure rise rate (MPRR) characteristics such as 0.8MPa/deg at IMEP 1.4MPa condition. The earlier combustion phasing led to the higher thermal efficiency characteristics of MPCI combustion compared with PPCI and CDC. This was attributed to the lower exhaust heat loss characteristics. However, high level of hydrocarbon (HC) and carbon monoxide (CO) emissions with low combustion stability at the low load operation were considered as severe challenges to overcome.