Cold Start Conditions Research Articles

Ozone-Catalytic Treatment of Automotive Exhaust

In the paper, an original design of an ozone-catalytic device, in which the process of ozone formation occurs directly inside the catalyst monolith of the honeycomb structure, is proposed for solving the problem of exhaust gases purification at the "cold start" of an automobile engine. For the considered device, various regimes of operation were examined, and the equations allowing us to calculate the concentrations of ozone depending on time were obtained. The developed mathematical model shows a significant decrease in ozone concentration after the "cold start" is over and the temperature of the exhaust gases increases, because of changes in the balance of various chemical reactions. Thus, the ozone concentration is maximum during a cold start, precisely when the lower temperatures do not allow other reactions than those of oxidation of toxic gases with ozone, and decreases by the time the catalytic unit warms up, when effective neutralization of toxic impurities becomes possible without the participation of ozone. The results of the mathematical modeling were confirmed by testing this device for purifying exhaust gases of a YaMZ-238M2 engine. The test results show that the use of ozone-catalytic reactions significantly increases the efficiency of neutralizing toxic impurities under cold start conditions, compared to the case when only catalytic reactions with oxygen without the participation of ozone are used.

A novel valve strategy for particulate matter reduction in a gasoline direct injection engine operated at cold conditions

In this study, we proposed a novel intake strategy to reduce Particulate matter (PM) emissions from gasoline direct-injection (GDI) engines during cold-start conditions emissions. This strategy is characterized by generating strong intake turbulence and low in-cylinder pressure during fuel injection through delayed intake valve opening, which theoretically promotes fuel atomization and fuel-air mixture, thereby suppressing PM formation during combustion. Experiments were conducted on a single-cylinder GDI research engine, operating at 1500 rpm, 3, 6, and 8 bar IMEP, and stoichiometric air-fuel ratio conditions with low coolant and lubricant temperatures to experimentally demonstrate the effectiveness of the proposed valve strategy in reducing PM emissions. Benchmark tests were performed using an intake camshaft with intake valve opening (IVO) at −13 °aTDC and intake valve closing (IVC) at 227 °aTDC. The novel strategy uses an intake camshaft with very late IVO at 66 °aTDC and IVC at 226 °aTDC. Two injection pressures (Pinj = 100/200 bar) were used to evaluate the pressure requirement for achieving low PM emissions with both strategies. Start of injection was swept and optimized to match the valve strategy. The results showed that the novel valve strategy leads to a 50%–90% reduction in particle number and mass emissions in cold-start conditions, and a lower injection pressure requirement to achieve comparable particle number and mass emissions compared with the normal one. For the novel valve strategy, the fuel impingement with early injection timings is largely mitigated, and thus an early injection timing shortly before the IVO is recommended.

IPSRM: An intent perceived sequential recommendation model

Objectives:Sequential recommendation aims to recommend items that are relevant to users’ interests based on their existing interaction sequences. Current models lack in capturing users’ latent intentions and do not sufficiently consider sequence information during the modeling of users and items. Additionally, noise in user interaction sequences can affect the model’s optimization process. Methods:This paper introduces an intent perceived sequential recommendation model (IPSRM). IPSRM employs the generalized expectation–maximization (EM) framework, alternating between learning sequence representations and optimizing the model to better capture the underlying intentions of user interactions. Specifically, IPSRM maps unlabeled behavioral sequences into frequency domain filtering and random Gaussian distribution space. These mappings reduce the impact of noise and improve the learning of user behavior representations. Through clustering process, IPSRM captures users’ potential interaction intentions and incorporates them as one of the supervisions into the contrastive self-supervised learning process to guide the optimization process. Results:Experimental results on four standard datasets demonstrate the superiority of IPSRM. Comparative experiments also verify that IPSRM exhibits strong robustness under cold start and noisy interaction conditions. Conclusions:Capturing latent user intentions, integrating intention-based supervision into model optimization, and mitigating noise in sequential modeling significantly enhance the performance of sequential recommendation systems.

An efficient product design tool for aftertreatment system

A numerical simulation technique based on the conservation of mass and energy in the gas phase has been developed to optimize the aftertreatment system with the lowest costs. Both oxygen storage capacity model and catalyst deterioration model have been integrated into the three-way catalyst performance model. Applications have been discussed, including XY-L 1.5L I3 gasoline turbocharged direct injection (GTDI) production hybrid vehicle, BY-L 1.5L I4 GTDI hybrid vehicle, XY-L (overseas version) 1.5L I4 GTDI hybrid vehicle, and G-L7 1.5L I4 GTDI hybrid vehicle. Vehicle tests in support of the proposed model have been described. The developed model covers the complete range of the cold start, high temperature and volume flow conditions. To optimize a three-way catalyst performance, this work simulated the effect of air fuel ratio, space velocity, temperature, biasing adjustment on the catalyst efficiency. The simulations presented the technique’s capability of well predicting emissions on fresh and full useful life aged aftertreatment systems, respectively, and carried out under transient conditions. The investigation indicated that excess fueling was used upon engine start to heat the catalyst up to its full operating temperature of greater than 350°C. The model results prompted a redesign of the I3 and I4 1.5L GTDI China 6b, Euro VId and Tier 3/SULEV30 exhaust systems over the world light vehicle test procedure (WLTP) and federal test procedure (FTP) cycles, respectively, for example, the model suggested that the latest design for the SULEV30 aftertreatment system on XY-L (overseas version) 1.5L I4 GTDI hybrid vehicle with the revised calibrations in the areas of cold-start and closed-loop fuel treated emissions of NMOG, NOx, and CO to the 70% of the SULEV30 standards with a $64 cost reduction relative to the baseline.

Hybrid attribute-based recommender system for personalized e-learning with emphasis on cold start problem

This article introduces a recommendation system that merges a knowledge-based (attribute-based) approach with collaborative filtering, specifically addressing the challenges of the pure-cold start scenario in personalized e-learning. The system generates learning recommendations by assessing item similarities, utilizing the Rogers-Tanimoto similarity measure for materials and users, and Jaccard's similarity for user comparisons. Unlike traditional collaborative methods relying on prior ratings, this approach depends on attributes. Additionally, user and learning material profiling structures were created to serve as fundamental inputs for the recommendation algorithm. These profiles represent student and material knowledge in a two-dimensional space to facilitate matching. Our processes incorporate user learning styles, preferences, and prior knowledge as metrics for achieving the desired level of personalization. The system produces a list of top recommendations based on predicted ratings. To validate its efficacy, a website resembling our learning platform was developed and tested by users. The primary results demonstrate the system's ability to identify similar users even in a pure cold start condition without existing ratings. Consequently, the system proves its capability in recommending suitable materials, modeling students, and identifying similar user groups. The evaluation results of the proposed system showed a good level of satisfaction by the testimonials, quantified by a score of 82% for the recommended materials (16% higher than exiting cold-start systems), and an average score of 90% in terms of satisfaction about the generated student profiles. As they proved the capability of the framework in recommending suitable materials, and its capability in modeling students, finding similar groups of users.

Studi Numerik Pengaruh Penambahan Turning Vane Terhadap Bentuk Aliran dan Distribusi Temperatur di Heat Recovery Steam Genertor (HRSG)

Tanjung Uncang Power Plant is one of the facilities in Indonesia that utilizes CCGT (Combined Cycle Gas Turbine). This cycle uses an HRSG (Heat Recovery Steam Generator) to heat steam using the exhaust gases from the gas turbine. At Tanjung Uncang's HRSG, the SOP requires that the gas turbine exhaust during cold start conditions must be below 400°C. Meanwhile, the gas turbine at Tanjung Uncang has a base load of 5 MW with a temperature range of 560°C - 580°C. Therefore, an asynchronous process is necessary to reach the FSNL (Full Speed No Load) condition for the gas turbine, with the damper angles set at 51°, 68°, and 90° for 45 minutes. Additionally, to achieve optimal conditions with the gas turbine running at 45 MW, a time span of 8 hours is required, which results in losses of up to 700 million. The extended time required can be due to uneven flue gas distribution, necessitating time for the HRSG to reach optimal conditions. This underscores the need to analyze the effects of adding turning vanes with angles of 35°, 53°, and 71°, and inlet temperatures of 400°C and 580°C on the characteristics of flue gas distribution. The analysis was conducted using CFD with ANSYS Fluent 2021 software. The simulation outputs include velocity vectors, velocity contours, and temperature distribution contours.

Effects of continuous variable valve timing and duration on fuel/air mixture formation

With increasing global regulations on particulate emissions, the particulate matter and number released under cold start and high-load conditions have become crucial. Under such conditions, the particulate emissions from port fuel injection engines can be significant and comparable to those from gasoline direct injection engines. In this case, fuel evaporation and mixture formation contribute to the reduction in particulate emissions. One method to improve these characteristics is to enhance the in-cylinder flow and turbulence kinetic energy. Therefore, in this study, we investigated the effect of in-cylinder flow enhancement on the particulate emissions reduction in port fuel injection engines. Simulations were conducted with various intake valve timings and durations under cold-start conditions. We then performed engine experiments to confirm the reduction in particulate number. The results showed that the relationship between the intake valve open timing and piston speed was crucial. Opening the intake valve to its maximum value slightly after the point of peak piston velocity resulted in a higher flow intensity and turbulence kinetic energy during the compression stroke. In addition, the experimental results indicated that improving the in-cylinder flow using continuous variable valve timing reduced the particulate number by 27.51 %.

Experiments and modeling of the thermal spray-chasing phenomenon during split injection processes

Spray chasing is a specific manifestation of the interaction between split injections, where the mass and heat transfer between the pilot and main sprays significantly influence fuel mixing and ignition processes. In this study, a spray-chasing model is developed and validated based on optical diagnostic results, aiming to theoretically support the development of injection strategies that are more environmentally adaptive and offer improved performance. A series of optical diagnoses of diesel split injection is performed in a constant volume combustion chamber using diffused back-illumination imaging and high-speed schlieren imaging. The extent of the spray-chasing phenomenon is modulated by regulating the injection dwell time (DT) and ambient temperature. For inert sprays, when the background temperature exceeds 790 K, the liquid spray-chasing phenomenon can be disregarded owing to the premature evaporation of the pilot spray. Although shortening the DT can promote the development and mixing of the main spray, the lack of evaporation in the pilot fuel pocket leads to a higher local fuel concentration in the interaction zone after spray chasing, which will hinder the subsequent ignition of the main spray. For reactive sprays, the variations in spray chasing patterns under different operating parameters are determined and their impact on the ignition process is evaluated by combining optical test results with theoretical models. Under cold start conditions, the ignition delay and ignition location of the main spray exhibit a non-monotonic trend with increasing injection dwell time. Optical diagnosis observes that compared to DT of 200 us and 1500 μs, the main spray exhibits both valley in ignition delay time and ignition location at DT = 900 μs. The spray-chasing model identifies approximately 1020 μs as the optimal theoretical DT, expected to best facilitate ignition of the main spray. However, under hot-start conditions, even though the spray-chasing mode varies with different injection dwell times, the ignition characteristics remain essentially unchanged due to the limited promotion effect of split injection on ignition.

Spray autoignition study of bio-oxygenated additives blended with aviation kerosene under engine-like cold-start conditions

Abstract Bio-oxygenated fuels are expected to be used as a clean alternative energy source to improve the ignition behavior and pollutant emissions of RP-3 kerosene in compression ignition engines. In this study, the spray autoignition of PR-3 blended with different types of oxygenated fuels (including n-pentanol (PeOH), methyl propionate (MP), methyl ethyl ketone (MEK), 1,2-dimethoxyethane (1,2-DME), and 2-Ethylhexyl nitrate (EHN)) was measured using a constant-volume combustion chamber. Experiments were performed on three sets of blended fuels with different oxygen contents (2.5 wt%, 5 wt%, 10 wt%) in the temperature range of 723∼863 K and at ambient pressures of 2.2 and 4 MPa. A kinetic analysis utilized a merged RP-3 low-temperature kinetic model containing various oxygenated components. The ignition delay of blended fuels increases with the addition of PeOH, MP, and MEK, particularly PeOH, which demands more energy absorption at low temperatures due to its higher specific heat and latent heat of vaporization. As ambient pressure increased, the ignition delay period shortened for all blended fuels; however, PeOH and MEK demonstrated more significant low-temperature suppression. The combined kinetic model can reasonably predict the trend of the effect of oxygenated additives. 1,2-DME showed significantly more low-temperature reactivity versus PeOH, MP, and MEK. The variability is because the products of secondary O2 addition and isomerization of 1,2-DME undergo low-temperature branched chain reactions, but other oxygenated fuels produce more inert components.

Characterizing ammonia emission from light-duty gasoline vehicles under the influence of multiple factors and its correlation with conventional pollutants

Ammonia (NH3), which is a precursor of secondary particulate matter (PM), can be produced through three-way catalyst (TWC) side reactions in light-duty gasoline vehicles (LDGVs), posing a threat to human health and air quality. To explore ammonia emission characteristics, 8 LDGVs and 1 hybrid electric light-duty vehicle (HEV) with various mileages traveled were analyzed with a chassis dynamometer system during regulation driving cycles. The emission factors of the adopted China VI in-use LDGVs were 7.04 ± 2.61 mg/km under cold-start conditions and 4.94 ± 1.69 mg/km under hot-start conditions. With increasing mileage traveled, the total ammonia emissions increased, and the difference between the cold/hot-start results decreased. The emissions of in-use LDGVs with bi-fuel engines were analyzed, and more ammonia was generated in the compressed natural gas (CNG) mode through the hydrocarbon (HC) reforming reaction. The relationship between the emissions of ammonia and conventional pollutants was established. During the initial cold-start phase, a delay in ammonia formation was observed, and the ammonia emissions conformed with the CO and HC emissions after exhaust heating. Vehicle specific power (VSP) analysis revealed that the interval of highest ammonia emissions corresponded to acceleration events at high speeds. For the HEV, the transition from motor to engine drive conditions contributed to ammonia emission occurrence because of the more pronounced cold-start events. The use of HEV technology could introduce additional uncertainties in controlling urban ammonia emissions. Detailed analysis of emission characteristics could provide data support for future research on ammonia emission standards and control strategies for LDGVs.

Analysis of energy consumption efficiency and emissions according to urban driving of hybrid electric vehicles in Korea

Internal combustion engines contribute significantly to global warming and air pollution in urban areas with high population densities and abundant vehicular movement. Alternative energy vehicle, such as hybrid and electric vehicles, are being developed to address these concerns. However, a gradual transition to electrification while maintaining the existing fuel infrastructure appears more feasible than the rapid proliferation of battery-powered electric vehicles. Hybrid electric vehicles are recognized as an important means of improving vehicle fuel efficiency and reducing carbon emissions by introducing changes in driving modes to enhance energy consumption efficiency. Catalyst activation does not occur in cold starts, making it challenging to control exhaust emissions. In Korea, urban driving patterns characterized by speeds below 60 km/h often results in insufficient catalyst activation. Therefore, research on the characteristics of urban driving and cold-start conditions is essential. This study analyzed the urban driving characteristics of domestic hybrid vehicles reflecting urban conditions through chassis tests and examined the variations in the external temperature and engine contribution to assess the control capability of the hybrid system. Confirming that minimizing the engine preheating time during cold starts and efficiently utilizing energy stored in the motor can enhance fuel efficiency and reduce exhaust emission rates.

Dynamic Characteristics of the Droplet Impact on the Ultracold Surface under the Engine Cold Start Conditions

Dynamic Characteristics of the Droplet Impact on the Ultracold Surface under the Engine Cold Start Conditions

Investigation of the dynamic interaction mechanism of split injections during the ignition process under diesel engine-like cold- and hot-start conditions

In a range of operating conditions with variable injection parameters, interactions among split sprays present uncertainties across both temporal and spatial dimensions. Understanding these dynamic interactions is crucial for optimizing injection strategies to improve both the performance and environmental adaptability of diesel engines. In this study, optical diagnostics and numerical simulations were conducted to explore the interaction mechanisms between split injections and their impact on the ignition process. Engine-like cold and hot-start operating conditions were configured, and four injection strategies, including a single injection, were examined. The findings reveal that ambient temperature influences split spray interactions by altering their ignition characteristics, while injection dwell time modifies these interactions by changing the combustion spatial and temporal phase between split sprays. Compared to a single injection, split injection promotes the ignition and combustion of the main spray such as shortening ignition delay, reducing ignition location, and increasing flame area, but this promoting effect weakens under hot-start conditions. When the main spray chases the pilot spray before ignition, it increases the local concentration and reduces the temperature upstream of the pilot spray plume. However, since the effect front fails to reach the expected ignition region before the pilot ignition occurs, the ignition of the pilot fuel pocket remains unaffected. Under cold-start conditions, the main ignition delay shows a non-monotonic trend, reaching its minimum at an injection dwell of 900 μs, where the pilot ignition provides the main spray with elevated local temperatures and an increased hydroxyl mass fraction. Under hot-start conditions, the temporal overlap of ignition in split sprays is enhanced, yet spatial interaction weakens. Despite varying degrees of pilot flame decay before the main spray ignites with increasing injection dwells, the thermal radiation emanating from their combustion elevates the local temperature in the interaction zone beyond 1200 K. Consequently, upon catching up with the pilot injection, the main spray mixture rapidly ignites through the high-temperature reaction pathway, rendering the ignition delay insensitive with injection dwells.

Development of a hydrogen free-piston engine generator for range extenders

Free-piston engine generator (FPEG), as an important branch of range extender, is a very competitive development direction. In this paper, a hydrogen-fueled opposed-piston FPEG is proposed, which adopts a mechanical-pressurized structure and a two-layer control strategy based on the inner and outer dead center. The prototype well meets the requirements of stable power generation and vehicle loading. The experimental tests have been conducted, which show that the pure hydrogen is successfully ignited under the cold start condition, the combustion efficiency and generation efficiency reach 30 % and 20 % respectively, and the peak pressure is close to 40 bar. However, the prototype was unable to enter the stable operation stage due to frequent misfire phenomena. Based on the above, the causes of abnormal combustion were discussed and the energy loss of the prototype was calculated. The prototype was simulated to run in the stable operation stage finally, and the future optimization scheme based on control strategy and structure was concluded.

A comprehensive investigation of injection strategies for improving diesel engine combustion under cold start development

Starting at cold temperatures ranging from -30°C to 0°C has been a concern for all diesel engines, especially for future diesel engines that need to meet tighter carbon emission standards. Combustion instability and increasing smoke emissions are rising concerns during the cold start of diesel engines. Cold ambient conditions cause long cranking periods or complete misfire events in diesel engines; therefore, they produce a large proportion of pollutants within the cylinder due to incomplete combustion. In this study, a comprehensive investigation of multiple injection strategies was conducted under cold-start conditions to identify an optimal injection strategy that improves diesel combustion stability, cold-startup performance, and decreases white smoke emissions at cold ambient temperatures. This study found that cold start-up performance can be improved by eliminating misfire and lowering time to clean up white smoke with a three-injection strategy (two pilots and one main injection, simply named Pilot-Pilot-Main).

Enhancing Student Performance Prediction on Learnersourced Questions with SGNN-LLM Synergy

Learnersourcing offers great potential for scalable education through student content creation. However, predicting student performance on learnersourced questions, which is essential for personalizing the learning experience, is challenging due to the inherent noise in student-generated data. Moreover, while conventional graph-based methods can capture the complex network of student and question interactions, they often fall short under cold start conditions where limited student engagement with questions yields sparse data. To address both challenges, we introduce an innovative strategy that synergizes the potential of integrating Signed Graph Neural Networks (SGNNs) and Large Language Model (LLM) embeddings. Our methodology employs a signed bipartite graph to comprehensively model student answers, complemented by a contrastive learning framework that enhances noise resilience. Furthermore, LLM's contribution lies in generating foundational question embeddings, proving especially advantageous in addressing cold start scenarios characterized by limited graph data. Validation across five real-world datasets sourced from the PeerWise platform underscores our approach's effectiveness. Our method outperforms baselines, showcasing enhanced predictive accuracy and robustness.

Impact of flash boiling spray on soot generation of a rich fuel–air mixture under various ambient pressures

Particulate emission is one of the critical challenges for the modern gasoine direct injection (GDI) engines. Especially under cold start conditions, the global equivalence ratio inside the cylinder is often set quite rich, leading to the generation of a large amount of soot. The fuel distribution state, such as homogeneous mixing and heterogeneous mixing with local rich pockets prior to the combustion is the key factor affecting soot generation under cold start conditions in GDI engines. Flash boiling injection, as a method to promote fuel air mixing, could be a potential solution to sooting problems of rich mixture combustion under cold start conditions. However, the unclear influences of flash boiling spray to fuel–air mixing state and subsequent soot generation pose a challenge to soot reduction in GDI engines. This work aims to study the effect of various flash boiling degrees on fuel–air mixture formation and subsequent soot generation utilizing a customized constant volume combustion chamber (CVCC) incorporated with the gasoline direct injection scheme under moderately cold start ambient temperature of 30 °C. A global high equivalence ratio of 1.7 representing extremely rich combustions under cold start conditions is selected for strong sooting propensity. By setting different fuel temperatures (Tf= 30 °C and 120 °C) and various ambient pressures (Pa= 40 kPa, 100 kPa and 160 kPa), various spray flash boiling states (subcooled, transitional flash boiling and flare flash boiling sprays) are achieved, and finally various fuel distribution states of rich mixtures prior to combustion are obtained. High speed color camera and soot sampling TEM grids were used to capture and evaluate the characteristics of spray atomization, combustion and soot aggregate structures. Based on this investigation, the effect of flash boiling degree on fuel–air mixing and subsequent soot generation is analyzed. The results show that flash boiling spray enhances fuel atomization and produces much more homogeneous rich mixture with smaller local rich pockets and richer global premixed gaseous portion. Over-rich global premixed mixture combustion is prone to nuclei inception and agglomeration, producing soot aggregates with small primary particles. While the local rich pocket combustion is prone to surface growth, producing larger primary particles. Flash boiling spray could reduce the size of soot particles under cold start conditions by generating smaller local rich pockets.

Study on transient thermal state of steel piston in diesel engine under cold start condition

The thermal load issue of pistons remains a topic of active research, especially the transient thermal state of steel pistons in diesel engines under cold start conditions has not been studied in depth. In this paper, a new steel piston power assembly was designed and developed on the basis of a small-bore diesel engine. A real-time temperature test system for the steel piston temperature field was developed to address the problem of the inability to obtain real-time temperature data. The test system was applied to the steel piston to investigate the transient variations in temperature field, thermal stress, and thermal deformation at different starting temperatures. The results show that the temperature field of steel pistons exhibits exponential growth in the early stage of cold start and then tends to stabilize after about 44 s. The lower the cold start temperature and the closer the monitoring points are to the high-temperature combustion gas, the faster the rate of temperature rise. The thermal stress of the steel piston initially increases rapidly, then decreases, and subsequently increases again until reaching a stable level. The lower the starting temperature, the longer the thermal stress inflection point of the monitoring point will be. The variation of thermal deformation of the steel piston follows the same trend as that of the temperature field.

Study on the forming process of the cylinder wall fuel film and the piston top land ablation mechanism of a medium speed marine diesel engine under cold start condition

The study presents an explanation of the piston top land ablation mechanism in a specific type of marine medium-speed diesel engine, utilizing multi-dimensional Computational Fluid Dynamics (CFD) software. At present, there is a lack of research on the process analysis of fuel droplets attached to the cylinder wall at diesel engine cold start condition and the mechanism of piston top land ablation. The study results indicate that during low-speed cold start condition, a multitude of diesel droplets impact the wall, causing the combustion area concentrated near the wall of the combustion chamber. The last stage fuel spray droplets, driven by the vortex in the cylinder, adhere to the cylinder wall before evaporation during the post-combustion stage. After multi-cycle operation of the diesel engine under cold start condition, the mass of fuel film adhering to the cylinder wall and the cumulative fuel mass on the top of the gas ring increase. As the engine getting warm, higher cylinder wall temperature leads to rapid evaporation of the fuel film on the cylinder wall and the gas ring. Deflagration happens when the fuel vapor burns under high temperature and high-pressure condition, and subsequent pressure oscillation destroys the thermal boundary layer of the piston top land. Piston material ablation happens under high temperature and high-pressure shock.

Design of A Portable Solid-Fuel Rocket Stove

The depletion of fossil fuels is a hot topic of discussion these days. This is due to the increasing use of fossil fuels in human life. In terms of the increase in fuel and gas prices, we realise that the energy consumption that is increasing from year to year is not balanced with the availability of energy sources, which affects households that use fuel in the cooking process. So a design was carried out to make an ergonomic solid fuel stove with the aim of not using fuel anymore in the cooking process, in this design, the stove is designed to be more flexible and get a portable biomass rocket stove design by considering social aspects, performance, local resources, economy, environmentally friendly. Biomass fuels are solids, liquids or gases produced from organic matter.. Biomass fuels used in solid fuel stoves such as firewood, charcoal, briquettes and pellets. Each biomass fuel has different properties and characteristics. The designed portable rocket stove consists of several main parts namely combustion chamber, chimney, air duct, pan spot and cassing, using stainless steel material. The test results include combustion chamber and water temperature during the process, thermal efficiency, combustion rate and specific fuel consumption under cold start and hot start conditions. After hot start, it is found that the use of a chimney on a portable stove designed using coconut shell fuel is more effective than without a chimney. Shorter boiling time of 1 minute, greater combustion rate of 0.13 grams/minute, higher thermal efficiency of 2% and lower specific fuel consumption of 9.11 grams/litre of water when the stove uses a chimney.