Cold-start Stage Research Articles

Study on the redistribution mechanism and secondary purge strategy of proton exchange membrane fuel cells

Effective control of membrane water content is essential for increasing the space for ice formation during the cold start stage and enhancing the success rate of start-up. Shutdown purge can effectively lower the membrane water content following fuel cell operation. However, during the cooling and standing process after purge, the rapid change in saturated vapor pressure can result in the redistribution of membrane dissolved water, leading to an increase in its content and a reduction in the success rate of cold start. Therefore, this study establishes a multidimensional, multiphase simulation model to comprehensively and thoroughly analyze the redistribution mechanism after purging and investigates the relationship between membrane water content and cold start. This is achieved by identifying the maximum membrane water content boundary during the cold start process and ultimately improving the success rate of cold start through a secondary purge strategy. The research results indicate that the membrane water content of the fuel cell increases from 2.31 to 8.31 after redistribution. During the cold start stage, the cold start success of the fuel cell under different environmental temperatures exhibits relatively specific boundary conditions, with the cold start process being closely related to the load current density and initial membrane water content. After implementing the secondary purging strategy, the membrane water content of the fuel cell decreases again, displaying favorable cold start characteristics in the cold start stage and successfully starting at −10 °C. This study can provide a reliable basis for the development of purging strategies during shutdown and offer a theoretical foundation for the boundary identification process of cold start.

Session context data integration to address the cold start problem in e-commerce recommender systems

Recommender systems play an important role in identifying and filtering relevant products based on the behaviours of users. Nevertheless, recommender systems suffer from the ‘cold-start’ problem, which occurs when no prior information about a new session or a user is available. Many approaches to solving the cold-start problem have been presented in the literature. However, there is still room for improving the performance of recommender systems in the cold-start stage. In this article, we present a novel method to alleviate the cold-start problem in session-based recommender systems. The purpose of this work is to develop a session similarity-based cold-start session alleviation approach for recommendation systems. The developed method uses previous sessions’ contextual and temporal features to find sessions similar to the newly started one. Our results on three different datasets show that, based on the provided Mean Average Precision and Normalised Discounted Cumulative Gain scores, the Session Similarity-based Framework consistently outperforms baseline models in terms of recommendation relevance and ranking quality across three used datasets. Our approach can be used to address the challenges associated with cold start sessions where no previously interacted items are present.

Improvement of the recommendation system based on the multi-armed bandit algorithm

In order to effectively solve common problems of the recommendation system, such as the cold start problem and dynamic data modeling problem, the multi-armed bandit (MAB) algorithm, the collaborative filtering (CF) algorithm, and the user information feedback are applied by researchers to update the recommendation model online and in time. In other words, the cold start problem of the recommendation system is transformed into an issue of exploration and utilization. The MAB algorithm is used, user features are introduced as content, and the synergy between users is further considered. In this paper, the author studies the improvement of the recommendation system based on the multi-armed bandit algorithm. The Liner Upper Confidence Bound (LinUCB), Collaborative Filtering Bandits (COFIBA), and Context-Aware clustering of Bandits (CAB) algorithms are analyzed. It is found that the MAB algorithm can get a good maximum total revenue regardless of the content value after going through the cold start stage. In the case of a particularly large amount of content, the CAB algorithm achieves the greatest effect.

An optical investigation on the effects of split-injection on hydrogenated catalytic biodiesel/gasoline dual-fuel engine under cold start conditions

Reactivity-controlled compression ignition (RCCI) mode has emerged as a promising technology for internal combustion engines, offering precise combustion phase control and the potential to meet stringent emission regulations. However, RCCI mode faces challenges, particularly misfiring during cold start conditions. This study proposes a solution by utilizing hydrogenated catalytic biodiesel (HCB) as a pilot fuel for gasoline and implementing a split-injection strategy to address the challenge. Experimental research was conducted on an optical engine under cold start conditions, incorporating three split-injection strategies: P30M70 (30 % main-injection and 70 % pilot-injection), P50M50, and P70M30. The results demonstrate that although gasoline can only be ignited by the main-injected HCB under coldstart conditions, the in-cylinder environment becomes more dynamic due to the pilot-injection. Consequently, split-injection reduces ignition delay by up to 7.09 °CA and shortens the combustion stage compared to single-injection. Among the various injection strategies examined, P30M70 demonstrated outstanding in-cylinder heat release performance, surpassing other split-injection strategies by up to 26.77 J/CAD, and outperforming the single-injection by 22.94 J/CAD. Visualization tests indicate that applying the P30M70 strategy leads to higher soot production under conditions of delayed main-injection timing (-15 °CA ATDC). However, the peak flame area under cold-start conditions is 53.16 % greater than P50M50 and 71.28 % greater than P70M30, highlighting excellent flame propagation characteristics. The average in-cylinder temperature suggests that a larger visible flame area contributes to engine warming. Despite the inherent trade-off, the dual-fuel mode of HCB/gasoline proves suitable for RCCI engines, with the P30M70 split-injection strategy being recommended for the cold start stage.

STEAMCODER: Spatial and Temporal Adaptive Dynamic Convolution Autoencoder for Anomaly Detection

The anomaly detection algorithm greatly improves the reliability of equipment operation. Traditional anomaly detection algorithms are mostly designed for large data sets, making it difficult to detect anomalies when where is not enough accumulated equipment data. Therefore, detecting anomalies during the cold-start stage is also challenging. In industrial production, the working conditions of the equipment are constantly adjusted, and the amount or characteristics of data for training also change frequently. Hence, an adaptive algorithm is required to address these problems. We design a novel algorithm called Spatial-TEmporal Adaptive dynaMic Convolution autoencODER for Anomaly Detection (STEAMCODER), specifically. This algorithm first converts the data into a spatial–temporal anomaly feature matrix and then utilizes a dynamic convolution autoencoder to analyze the matrix and detect anomalies. Finally, we conduct extensive experiments to validate the performance of STEAMCODER and the results demonstrated its superiority compared to state-of-the-art algorithms in adaptive anomaly detection, including F1 score and other indicators. Furthermore, STEAMCODER is capable of filtering false positives caused by glitch data, enabling the early detection of equipment anomalies.

Particulate Matter Load Estimation and Distribution Characteristics of Diesel Particulate Filter

This paper focuses on the offline electric heating regeneration technology of DPF (Diesel Particulate Filter). Based on the actual operating conditions of the airport passenger elevator, the pressure drop changes before and after the offline regeneration of DPF, the passive regeneration process during the vehicle operation, and the capture efficiency of PM and PN after the offline regeneration of DPF are studied. The DPF pressure drop increases with the operation time because of the extremely low efficiency of passive regeneration before offline regeneration, and the initial pressure drop after regeneration is slightly higher than that of the fresh carrier due to the existence of ash. When the exhaust temperature reaches 420°C, the DPF passive regeneration rate is higher than the capture rate, and the DPF pressure drop drops rapidly when the passenger elevator continues to run. The mass fraction of fine particulate matter is more than 0.02μm in the cold start stage, while the mass fraction of fine particulate matter is more than 0.02μm in the hot start stage.

Exhaust aftertreatment device-derived ammonia emissions from conventional and hybrid light-duty gasoline vehicles over different driving cycles

Ammonia emissions from motor vehicles have great effect on air pollution and human health in urban areas. Recently, many countries have focus on ammonia emission measurement and control technologies for light-duty gasoline vehicles (LDGVs). To analyze ammonia emission characteristics, three conventional LDGVs and one hybrid electric light-duty vehicle (HEV) were evaluated over different driving cycles. The average ammonia emission factor at 23℃ was 4.5 ± 1.6 mg/km over Worldwide harmonized light vehicles test cycle (WLTC). Most ammonia emissions mainly concentrated in low and medium speed sections at cold-start stage, which were related to rich burn conditions. The increasing ambient temperatures led to the decrease of ammonia emissions, but high load caused by extremely elevated ambient temperature led to obvious ammonia emissions. The ammonia formation is also related to three-way catalytic converter (TWC) temperatures, and underfloor TWC catalyst could eliminate ammonia partly. The ammonia emission from HEV, which are significant less than LDGV, corresponded to the engine working state. The large temperature difference in the catalysts caused by power source shifts were the main reason. Exploring the effects of various factors on the ammonia emission is beneficial for revealing the instinct formation conditions, providing theoretical support for the future regulations.

Experimental study on the emission characteristics and performance of PNA coupled aftertreatment system with different catalyst loading

In order to meet the strict emission regulations in the future, passive NOx absorber (PNA) and electrically heated catalyst (EHC) will gradually become the necessary technologies for diesel engines. In this paper, based on a diesel engine with PNA, EHC, diesel oxidation catalyst (DOC), selective catalytic reduction catalyst integrated into diesel particulate filter (SDPF) and selective catalytic reduction catalyst (SCR), the impact of PNA emission characteristics and performance with different catalyst loading were investigated. The results showed that EHC was coupled behind the DOC is more conducive to energy conservation and reducing NOx emissions. Compared with EHC was coupled in front of the DOC, the time for SDPF inlet temperature to reach 180 ℃ was reduced by 123 s, the power consumption of EHC was reduced by 0.25 kWh and nitrogen oxide (NOx) conversion efficiency increased by 16.61% in the cold start phase when EHC was coupled behind the DOC. Meanwhile, PNA has a certain adsorption effect on CO, THC, and NOx. When EHC was coupled behind the DOC, the adsorption amount of carbon monoxide (CO), total hydrocarbon (THC), and NOx increases with the increase of PNA catalyst loading. The maximum adsorption time of PNA for NOx reached 171 s. Similarly, the conversion efficiency of CO, THC, and NOx during the cold start stage also increases with the increase of PNA catalyst loading. The maximum average conversion efficiency of CO, THC, and NOx was 60.58%, 88.60%, and 95.72%, respectively. In cold start phase, the PNA50 has achieved high PNA performance, and the gain brought by higher catalyst loading is not obvious. In medium–high temperature phase, due to the high exhaust temperature, PNA has no effect on the conversion efficiency of CO, THC, and NOx. PN conversion efficiency is more than 99% and is not affected by the PNA type. The findings provide the fundamental insights to promote the application of PNA and EHC in diesel engines and reduce emissions of diesel engines under cold start conditions.

A mobile platform for characterizing on-road tailpipe emissions and toxicity of ultrafine particles under real driving Conditions

Acute exposure to fresh traffic-related air pollutants (TRAPs) can be high for road users, including motorbike drivers, cyclists, and pedestrians. However, evaluating the toxicity of fresh traffic emissions from on-road vehicles is challenging since pollution properties can change dynamically within a short distance and time. This study demonstrated a mobile platform equipped with an On-Board Diagnostic II (OBDII) system, a tailor-made portable emission measurement system, and an electrostatic air-liquid interface exposure system with human monocytic THP-1 cells to characterize on-road tailpipe emissions under real driving conditions. High number concentrations up to 106–107 # cm−3 of ultrafine particles (UFPs) were observed for a gasoline engine at the cold-start stage and a diesel engine during particulate filter regeneration. In particular, a substantial fraction of freshly emitted UFPs within the size less than 23 nm were observed and should be cautioned. The potential toxicity of fresh TRAPs was quantified by cell viability, cytotoxicity, oxidative stress, and inflammatory biomarkers. Results show that the decreased cell viability, increased lactate dehydrogenase (LDH) activity, and high oxidative stress induced by the fresh TRAPs were potentially contributed by gaseous pollutants as well as particles, especially driving with the high idling frequency. Moreover, the dominant contributor to the toxicity is different for gasoline's and diesel's TRAPs. Characterizing on-road air pollutant toxicity as well as physicochemical properties using an innovative mobile platform can fill this knowledge gap.

Analysis of passenger vehicle pollutant emission factor based on on-board measurement

With the increase in the number of vehicles, air pollution in Northeast China raised growing concerns. In order to understand the pollutant emissions of passenger vehicles, this study analyzes the influencing factors of emission factors from both the start-up stage and the operation stage, respectively. It was found that during the start-up stage, the emission factors were mainly influenced by emission standards, fuel type, initial engine temperature and environmental temperature; during the operation stage, the emission factors were mainly influenced by driving speed, road properties and time properties. The analysis shows that the contribution rate of start-up emission can be effectively reduced by increasing the initial engine temperature or using compressed natural gas fuel. In the cold start stage, the CO and NOx emission factors in winter are 23 or 6.37 times of those in autumn. For China 5 light-duty gasoline-fueled vehicle, the operating emission factors of CO2, CO, NOx and VOCs are 247.48 g/km, 0.493 g/km, 0.061 g/km and 0.084 g/km, respectively. For China 4 LDGVs, the operating emission factors of CO2, CO, NOx and VOCs are 252.118 g/km, 3.166 g/km, 0.426 g/km and 0.113 g/km, respectively. For China 5 compressed natural gas -fueled vehicles, the operating emission factors of CO2, CO, NOx and VOCs are 156.304 g/km, 1.131 g/km, 0.945 g/km and 0.477 g/km, respectively. To reduce the pollutant emission factors of vehicles, the government should promote China 6 vehicles and new energy vehicles, optimize the road layouts structure of the square loops and road intersections, and strictly implement the I/M (Inspect Maintenance) regulation.

Study on pollutant emission characteristics of different types of diesel vehicles during actual road cold start

The current regulations of heavy-duty vehicles in China do not include the emissions in the cold start stage into the overall emission evaluation. However, the speed of heavy-duty diesel vehicles in the cold start stage is often low and the proportion of idle-conditions is large, resulting in the difference between the actual test results and evaluation results of emissions. Therefore, in order to accurately evaluate the impact of emission during cold start on the overall emission, in this study, the OBS-ONE portable vehicle emission test equipment was used to test the emission of three representative heavy-duty diesel vehicles with different types under actual road driving conditions, and the cumulative averaging (CA) method was adopted to calculate and analyze the test emission data.Firstly, the cold start emission of different types of heavy-duty vehicles was evaluated. The results show that the contribution rate of pollutant emission in the cold start stage is high, in which NOx emission accounts for 40–90% of the whole trip. It was unreasonable for regulations to exclude data in the cold start stage. The cold start duration of vehicle A is nearly 300 s longer than that of vehicle C, however, the NOx and PN emission factors of vehicle A are nearly 10 times and 100 times smaller than that of vehicle C at the cold start stage respectively. The cold start duration, fuel consumption and the emission factors in cold start stage of different types of heavy-duty diesel vehicles do not have a unified law. Secondly, the emission characteristics and differences of different types of heavy-duty vehicles are studied at the instantaneous level, and the internal mechanism causing the emission differences is explored and revealed. In the cold stage, CO2 emission shows a good correlation with the fuel consumption. CO, NOx emissions show a good correlation with the fuel consumption when the engine and post-treatment temperature are low, and CO and NOx emissions decrease with the increase of engine and post-treatment temperature. PN emissions are mainly related to the engine working state. Finally, the influence of dynamic parameters v·a and RPA on pollutant emission was analyzed. The results show that driving force is an important factor affecting CO2 emission, and RPA has no obvious correlation with emission at cold start stage.

Deactivation of Pd/SSZ-13 by Potassium and Water for Passive NOx Adsorption

The passive NOx adsorber (PNA) material has been considered an effective candidate for the control of NOx from diesel exhaust during the engine cold start stage, and Pd/SSZ-13 attracts peoples’ attention mainly due to its superior hydrothermal stability and sulfur resistance. However, chemical poisoning tolerance of Pd/SSZ-13 is another key parameter to its practical application and future development. Herein, we prepared potassium-loaded Pd/SSZ-13 and evaluated the influence on NOx adsorption ability. The characterization results revealed that the loading of potassium could not destruct the structure of SSZ-13 but impaired the BET surface area and pore structure through the sintering of Pd species to PdO. Meanwhile, the grown PdO phase restrained the NOx adsorption ability and promoted the generation of NO2 at high temperatures. Moreover, the presence of H2O could also impair the NOx adsorption ability due to the competitive adsorption between H2O and NOx. This work verifies that the design of Pd/SSZ-13 sample with stable Pd species and excellent hydrophobicity is significant for its further application under harsh conditions.

Research on ammonia emissions characteristics from light-duty gasoline vehicles

In this study, ammonia emissions characteristics of typical light-duty gasoline vehicles were obtained through laboratory vehicle bench test and combined with New European Driving Cycle (NEDC) condition and Worldwide Harmonized Light Vehicles Test Cycle (WLTC) condition. The influence of ambient temperature on ammonia emissions is mainly concentrated in the cold start stage. The influence of ambient temperature on ammonia emission is shown that the ammonia emissions of light-duty gasoline vehicles under ambient temperature conditions (14 and 23°C) are lower than those under low ambient temperature conditions (−7°C) and high ambient temperature conditions (35 and 40°C). The influence of TWC on ammonia emission is shown that ammonia is a by-product of the catalytic reduction reaction of conventional gas pollutants in the exhaust gas in the TWC. Under NEDC operating conditions and WLTC operating conditions, ammonia emissions after the catalyst are 45 times and 72 times that before the catalyst, respectively. In terms of ammonia emissions control strategy research, Pd/Rh combination can reduce NH3 formation more effectively than catalyst with a single Pd formula. Precise control of the engine's air-fuel ratio and combination with the optimized matched precious metal ratio TWC can effectively reduce ammonia emissions.

Multi-Round Incentive Mechanism for Cold Start-Enabled Mobile Crowdsensing

Mobile CrowdSensing (MCS) has emerged as a novel paradigm for performing large-scale sensing tasks. Many incentive mechanisms have been proposed to encourage user participation in MCS. However, most of them ignore the inevitable cold start stage of MCS, where the MCS system has just begun releasing tasks. Also, they all adopt the single-round incentive without considerations of the continuous cumulative effect. Given the severe shortage of participants in the cold start stage of MCS, this paper proposes a Multi-Round Incentive Mechanism (MRIM). MRIM is based on monetary incentives by adopting multi-round cooperation and alternating between task information diffusion and task allocation operations, both of which are NP-hard problems even without inter-round coupling imposed by system budget constraints. We explore a method to predict the probability of users participating in tasks accurately. Furthermore, we present an efficient task information diffusion algorithm to maximize the number of users participating in tasks by submitting bids. We propose a fast task allocation algorithm based on truthful auction, comprising an approximation algorithm for solving the one-round winner selection and payment calculation. With budget constraints, MRIM maximizes the number of completed tasks by iteratively performing task information diffusion and task allocation. We also prove that MRIM also possesses desired properties such as computational efficiency, user rationality, platform profitability, and price truthfulness, which can further guarantee the robustness of MRIM. The extensive simulations conducted on real-world datasets have proved the efficiency of MRIM.

Research on exhaust emission characteristics and technical route under CLTC cycle

In this paper, the light duty that meets the China 6 emission standard is selected to study the emission characteristics of different emission control technology routes under China light-duty vehicle test cycle (CLTC). The results show that the cold start stage of CLTC cycle is still the stage with the most pollutant emissions. The THC, CO and NOx emissions of vehicles on the supercharged direct injection technology are higher than those on the naturally aspirated port fuel injection technology. In terms of reducing the exhaust emission, PHEV technology route is the best, followed by naturally aspirated PFI technology route, and then turbocharged direct injection with GPF route.

Wear resistance mechanism of engine piston skirt coating under cold start condition

At the beginning of cold start, the lubricating oil temperature is low, the kinematic viscosity is high, the splash lubrication effect is poor, and the good lubricating oil film cannot be formed, therefore, the friction and wear between piston and cylinder is serious. In this paper, the wear mechanism of aluminum alloy piston skirt coating was studied in the cold start stage with severe wear degree: the dynamic simulation and cold start test analysis were carried out for the skirt with or without coating, and the wear morphology, knife pattern structure and friction force were compared, so as to determine the friction reduction energy efficiency of the coating in the cold start stage.

Engine Performance and Emissions Analysis in a Cold, Intermediate and Hot Start Diesel Engine

Presented in this paper is an in-depth analysis of the impact of engine start during various stages of engine warm up (cold, intermediate, and hot start stages) on the performance and emissions of a heavy-duty diesel engine. The experiments were performed at constant engine speeds of 1500 and 2000 rpm on a custom designed drive cycle. The intermediate start stage was found to be longer than the cold start stage. The oil warm up lagged the coolant warm up by approximately 10 °C. During the cold start stage, as the coolant temperature increased from ~25 to 60 °C, the brake specific fuel consumption (BSFC) decreased by approximately 2% to 10%. In the intermediate start stage, as the coolant temperature reached 70 °C and the injection retarded, the indicated mean effective pressure (IMEP) and the brake mean effective pressure (BMEP) decreased by approximately 2% to 3%, while the friction mean effective pressure (FMEP) decreased by approximately 60%. In this stage, the NOx emissions decreased by approximately 25% to 45%, while the HC emissions increased by approximately 12% to 18%. The normalised FMEP showed that higher energy losses at lower loads were most likely contributing to the heating of the lubricating oil.

Characteristics of the transient thermal load and deformation of the evacuated receiver in solar parabolic trough collector

As a core element in solar parabolic trough collector, the evaluated receiver often runs under severe thermal conditions. Worse still, the transient thermal load is more likely to cause structural deformation and damage. This work develops an efficient transient multi-level multi-dimensional (M2) analysis method to address photo-thermal-elastic problems, thereby estimating transient thermal load and deformation for the receiver: (i) one-dimensional (1-D) thermo-hydraulic model is adopted to determine the transient thermo-hydraulic state, (ii) 3-D finite volume method (FVM) model for the receiver tube is established to obtain the real-time temperature distribution, (iii) 3-D finite element method (FEM) model is employed to make thermoelastic analysis. Based on this M2 method, the typical transient cases are conducted in cold-start, disturbed-operation and regulated-process. Three indicators (average temperature of the wall (ATW), radial temperature difference (RTD), circumferential temperature difference (CTD)) are defined for overall analysis of the receiver thermal load. It is found that in the transient process, receivers face response delay and endure significant thermal load fluctuation. The response time for a single HCE (heat collecting element) under lower mass flow rate (1.5 kg s−1) could sustain 280 s. During the cold-start stage (DNI=200 W m−2 to 800 W m−2), the maximum value of CTD in receiver is as high as 11.67°C, corresponding to a maximum deflection of 1.05 cm. When the mass flow rate decreases sharply by 80%, the CTD reaches 33.04°C, causing a 2.06-cm deflection. It should be pointed out that in the cold-start stage and the lower mass flow rate operation for solar parabolic trough collector, alleviating the transient thermal load and deformation is of importance for safely and efficiently running evaluated receiver.

Fast removal of pollutants from vehicle emissions during cold-start stage

Abstract Recently, enormous research passion has been devoted to reduce air pollution caused by vehicle emissions. Effective vehicle emission control method is to convert exhaust pollutants by placing catalyst in the exhaust pipe. However, the major stumbling block is that a large portion of emission occurs in the initial 20–30 s during the engine cold-start stage, before catalyst can reach its operating temperature. To address the challenge, herein we developed a catalyst utilizing Pd and Rh as active components, Ce-Zr solid solution as assistant, γ-Al2O3 as coating and Fe-Cr-Al as supporter. The catalyst component was optimized (atom ratio of Ce:Zr is 6:4, mass ratio of Pd:Rh is 8:2, total weight of Pd and Rh is 1.2 g/L, pore density is 700 pores/inch2) and high-frequency electrical heating technique was employed to decrease operating temperature from 400°C to 350°C and improve exhaust conversion efficiency by 78%.

Effect of partial-heating of the intake port on the mixture preparation and combustion of the first cranking cycle during the cold-start stage of port fuel injection engine

Abstract For Port Fuel Injection (PFI) engines, excessive fuel is needed for the first few cycles during the cold-start because of the unfavorable evaporation environment. The excessive fuel usually forms a fuel film which causes non-uniform mixture and becomes a major source of the Engine-Out Hydrocarbons (EOHC). In this paper, a partial-heating method was proposed to improve the evaporation of the deposited fuel film at the beginning of the cold-start of PFI engine. The partial-heating method focuses on increasing the surface temperature of the intake port end before the cranking start. In this study, the effect of the partial-heating was researched based on the first cranking cycle. The effect was experimentally investigated and discussed in terms of the mixture preparation, combustion and EOHC. The results showed that within the capacity of the on-board battery, the partial-heating led to efficient and effective heating of the surface of the intake port end. The fuel delivery efficiency was increased by over 10%. Fuel enrichment was reduced from 40 ms FPW to 30 ms FPW within 15 s of the partial-heating. Moreover, the mixture was found to burn faster in the partial-heating cases. Higher Indicated Mean Effective Pressure (IMEP) could be obtained with optimized spark timing in the partial-heating cases.