Cold Start Behavior Research Articles

Residential wood heat in the US: Results of a survey investigating user behavior and operation of wood heating appliances

Wood is used as a source of primary and secondary heat by millions of people in the US, but many wood stoves emit levels of particulate matter that negatively impact human health and the environment. Modern wood stoves are designed to pass emissions testing required by regulatory bodies and manufacturers may be hindered in their ability to design for the variability of real-world use. User behavior can strongly impact wood heater emissions, and learning about how they are used in real life could inform the future design of cleaner-burning wood heaters. In this study a survey was performed to investigate the habits, needs, and challenges surrounding residential wood heating in the US. Common user characteristics and behaviors are investigated in categories covering heating technology, fuel use and preference, user behavior, and operation. The data collected from 210 completed survey responses can be used to support and refute anecdotal understandings of wood stove use. Results from this study cover wood heater ages and the presence or lack of catalysts. Fuel provenance, type, seasoning, and storage practices are discussed, along with the ways that respondents learned how to use their stoves and their operational practices including reloading, cold start behavior, and use of air controls. The information presented in this paper can be used to inform industry and regulatory groups as to how people use their wood heaters and highlights areas for potential future research.

Simulation-Based Prediction of the Cold Start Behavior of Gerotor Pumps for Precise Design of Electric Oil Pumps

Simulation-Based Prediction of the Cold Start Behavior of Gerotor Pumps for Precise Design of Electric Oil Pumps

High-speed low-coherence interferometry of fuel films in impinging gasoline direct injection sprays

Quantitative experimental characterization of dynamic fuel film deposition processes is critical to developing better understanding and modeling of cold-start behavior in gasoline direct injection engines. Low-Coherence Interferometry (LCI) offers a quantitative fuel film thickness diagnostic that is immune or resistant to major confounding influences that limit other optical diagnostics in engine-relevant environments. This work describes an extension of spectral LCI techniques to high-speeds (10 kHz) that are capable of resolving the dynamics of fuel film deposition and evaporation in impinging gasoline sprays. Two approaches to LCI, Michelson interferometry and Fizeau interferometry, were tested and results demonstrate the superiority of the Fizeau configuration for enclosed vessel experiments. Experiments were performed at cold start conditions in an enclosed spray chamber with a gasoline spray impinging on a transparent wall. High-speed LCI was used to measure fuel film thicknesses and dynamic changes in thickness. The measurements were used to observe variation in film thickness and behavior with changes in system temperature and fuel composition.

The Effect of Spark-Plug Heat Dispersal Range and Exhaust Valve Opening Timing on Cold-Start Emissions and Cycle-to-Cycle Variability

<div class="section abstract"><div class="htmlview paragraph">The partnership for advancing combustion engines (PACE) is a US Department of Energy consortium involving multiple national laboratories and includes a goal of addressing key efficiency and emission barriers in light-duty engines fueled with a market-representative E10 gasoline. A major pillar of the initiative is the generation of detailed experimental data and modeling capabilities to understand and predict cold-start behavior. Cold-start, as defined by the time between first engine crank and three-way catalyst light-off, is responsible for a large percentage of NOx, unburned hydrocarbon and particulate matter emissions in light-duty engines. Minimizing emissions during cold-start is a trade-off between achieving faster light-off of the three-way catalyst and engine out emissions during that period. In this study, gaseous and soot emissions were measured at a distance representative of the three-way catalyst position downstream of the engine at a 2 bar net indicated mean effective pressure (NIMEP) steady-state operating condition representative of cold-start. The test matrix included sweeps of ignition timing 15 degrees-before to 10 degrees-after top dead center firing (TDC<sub>f</sub>) across three different spark-plug heat dispersal ranges (HR). Additionally, the effect of varying exhaust valve opening (EVO) timing on combustion stability and emissions was also studied. Results show that the spark plug HR affects the coefficient of variation (COV) of NIMEP under all cold-start conditions, while the impact on emissions was found to be minimal. At very retarded spark timings, colder spark plugs required higher air and fuel flow to maintain the desired 2bar NIMEP load, but the fraction of fuel energy going into the exhaust was found to be similar for all spark plugs. Retarding exhaust valve timings showed a simultaneous reduction in emissions while increasing the fraction of fuel energy being fed into the exhaust. However, engine COV was also observed to increase with retarded exhaust timings.</div></div>

Analysis of the cold start behavior of a polymer electrolyte membrane fuel cell in constant power start‐up mode

Analysis of the cold start behavior of a polymer electrolyte membrane fuel cell in constant power start‐up mode

Cold start behavior and freeze characteristics of a polymer electrolyte membrane fuel cell

AbstractVehicle applications require efficient cold start ability and durability of polymer electrolyte membrane fuel cells (PEMFCs). In this study, various self‐cold start strategies including purging the PEMFC at shutdown and using galvanostatic operation at startup are proposed. The cold start characteristics from −5°C of a single cell are experimentally investigated in situ on a laboratory scale. The amount of cumulated charge transfer density, corresponding to the amount of product water, is used as an index to quantify the cold start capability. Gas purge at shutdown before freeze is found to facilitate the PEMFC cold start, although the improvement is relatively small compared with other methods such as gradually increasing the current during startup. Microscopic studies of the membrane electrode assembly (MEA) after cold start failure are conducted to determine material degradation due to ice formation.

A CFD study of ignition of lean propane-air mixtures in a heat recirculating U-bend catalytic microreactor

Heat recirculating (HR) geometries have been studied in the literature for their use in energy generation applications. This work investigates the ignition and cold-start behavior of lean propane-air combustion in a U-bend catalytic microreactor through computational fluid dynamics (CFD) study. Although several studies have focused on stability and combustion behavior, the role of heat recirculation on catalytic and homogeneous ignition from the cold-start conditions has not been analyzed so far. The U-bend microreactor is a typical example of HR geometry, where the hot exhaust gases in the recirculation channel transfer heat to the cold incoming fluid. Significance of heat recirculation across the dividing wall on the ignition temperature, as well as transient evolution of temperature, propane conversion and reaction are presented. Ignition temperature is found to be 20K lower in the U-bend microreactor than straight channel microreactor. However, transient ignition study revealed that at nominal conditions, U-bend microreactor takes about 35s longer than straight channel for ignition and to reach steady state, owing to heat distribution internally within the U-bend microreactor. The effect of flowrate is analyzed, which shows that at higher flowrates, the ignition and steady-state times are also lower for the U-bend microreactor. Finally, the effect of solid wall material is investigated, which shows that lower conductivity material (such as ceramic) showed faster ignition with low thermal inputs.

Combining machine learning with 3D-CFD modeling for optimizing a DISI engine performance during cold-start

This work presents a methodology for using machine learning (ML) techniques in combination with 3D computational fluid dynamics (CFD) modeling to optimize the cold-start fast-idle phase of a gasoline direct injection spark ignition (DISI) engine. The optimization process implies the identification of the range of operating parameters, that will ensure the following criteria under cold-start conditions: (1) a fixed IMEP of 2 bar (BMEP of 0 bar), (2) a stoichiometric exhaust equivalence ratio (based on carbon-to-oxygen atoms) to ensure the efficient operation of the after-treatment system, (3) enough exhaust heat flux to ensure a rapid light-off of the after-treatment system, and (4) reduced NOx and HC emissions. A total of six operating parameters will be identified as having a significant influence on cold-start engine performance. These parameters are associated with the fuel injection strategy (end of the second injection, injection pressure, and fuel mass); combustion strategy (spark timing, spark energy); and intake airflow (intake manifold pressure). Performing an optimization study exclusively using multi-cycle (at least 3 cycles) 3D CFD simulations would be an arduous task. For example, to achieve an exhaust equivalence ratio of 1 and an IMEP of 2 bar, multiple iterations would be required for fuel mass (to account for film formation), intake manifold pressure (to ensure enough air in-cylinder), and spark timing (to ensure the fixed load). This process would be more convoluted and expensive with the addition of constraints for exhaust heat flux and emissions. A promising approach to tackling such a complicated optimization process is to employ the concept of machine learning, which demands a database formed by the six operating parameters mentioned above. The current work will demonstrate a strategy of combining CFD modeling with advanced Gaussian Process Regression (GPR)-based ML models to make predictions about DISI cold-start behavior with acceptable accuracy and a substantially reduced computational time.

Characteristics of Cold Start Behavior of PEM Fuel Cell with Metal Foam as Cathode Flow Field under Subfreezing Temperature

ABSTRACT Cold start has been realized as an important issue for PEMFC in its global commercialization. As is well-known, the conventional “channel-rib” type flow field will surely lead to several problems, such as water accumulation under the rib, resulting in slow water removal and serious ice blockage in the pores. In recent years, with the fast development of metal foam materials, metal foam has been recognized as a promising alternative replacement of the conventional “channel-rib” type flow field. In this study, a cold start model of PEMFC is established under sub-zero temperature. The coupled transport processes of heat, mass and charge in PEMFC under various subzero temperatures and startup modes are simulated. The results show that ice formation is slower in the PEMFC with metal foam as cathode flow field in cold start process, due to the superior performance of metal foam in water removal and uniform distribution of gas supply. However, the excellent thermal conductivity of metal foam could also result in faster heat loss from PEMFC. Furthermore, ice formation is highly dependent on the supercooled water transfer behavior, though small amount of supercooled water is maintained in the cell. This work aims to provide a systematic analysis for the cold start behavior of PEMFC with metal foam flow field.

Imaging and Quantification of Water inside Membrane-Electrode Assembly of Polymer Electrolyte Fuel Cell during Power Generation By Use of Neutron Beam

The polymer electrolyte fuel cells (PEFCs) have attracted attentions as energy-conversion devices of high power density with no emission of carbon dioxide. For the efficient and stable power generation of a PEFC, the water management inside the membrane-electrode assembly (MEA) is very important. A proper water management can adequately moisten the electrolyte membrane and improve the performance of a PEFC, while an excessive water can block the flow channels and the pores in gas diffusion layers (GDLs), as well as the catalyst layers; the mass transports are inhibited from the flow channels to the Pt catalysts resulting in a poor power generation. In case of large liquid water accumulations, the performance of the power generation is temporary decreased.1 Neutron imaging techniques have been used for understanding the distribution of liquid water inside PEFCs, and water droplets within the pores of the GDL and/or on the flow-channel walls have been mainly reported.2–4 However, the distribution of smaller amounts of water contained in catalyst layers or an electrolyte membrane has not been reported, which is very important because of the large effect on the mass transport inside the MEA.The visualization of water in an MEA was carried out using a pulse neutron beam at BL22 (RADEN) of MLF, J-PARC, Japan 5. The neutrons with the wavelength of 5-13.5 Å was separated and used to increase the attenuation of the neutron beam by water. A PEFC with 10 straight channels, 30 mm in length and 1 mm in width, was used. The endplates and current collectors were made of aluminum alloy (A7075) for the neutron penetration. The transmitted neutrons were converted to photons by a scintillator (ZnS(Li)) for imaging with a CCD camera. The neutron beam size was 102.4 mm ×102.4 mm (2048×2048 pixels), while a plate containing boron carbide (B4C) powders was used for a window of 50 mm × 50 mm to reduce the unpreferable radio activation of the cell. The cell temperature was kept at 80 oC. To obtain the background image, a dry N2 gas was supplied both to the anode and the cathode. Figures 1(a) and 1(b) show the background image under the dry condition and the image of water in the MEA at 100% RH (obtained by the division by the background image using an “ImageJ” software), respectively. The values at pixels aligned in the perpendicular direction in the area surrounded by yellow solid lines in Fig. 1(b) were integrated to be shown in Fig. 1(c). The neutron transmittance at the MEA shown by a red rectangle in Fig. 1(b) was lower than that in the other area. In this way, water in the MEA was detected by neutron imaging for the first time. The imaging of water during the power generation is now in progress, along with the qualification of water.Reference Hirakata, S. et al. Investigation of the effect of pore diameter of gas diffusion layers on cold start behavior and cell performance of polymer electrolyte membrane fuel cells. Electrochim. Acta 108, 304–312 (2013).Kramer, D. et al. In situ diagnostic of two-phase flow phenomena in polymer electrolyte fuel cells by neutron imaging: Part A. Experimental, data treatment, and quantification. Electrochim. Acta 50, 2603–2614 (2005).Turhan, A. et al. Quantification of liquid water accumulation and distribution in a polymer electrolyte fuel cell using neutron imaging. J. Power Sources 160, 1195–1203 (2006).Park, J. et al. Neutron imaging investigation of liquid water distribution in and the performance of a PEM fuel cell. Int. J. Hydrogen Energy 33, 3373–3384 (2008).Shinohara, T. et al. The energy-resolved neutron imaging system , RADEN. Rev. Sci. Instrum. 91, 043302 (2020). AcknowledgmentThis study was supported by Japan Science and Technology Agency (JST) and “SPer-FC Project” of New Energy and Industrial Technology Development Organization (NEDO). The neutron imaging was performed at BL22 (RADEN) of J-PARC (Proposal No. 2019A0217). Figure 1

Improving computational fluid dynamics modeling of Direct Injection Spark Ignition cold-start

Developing a profound understanding of the combustion characteristics of the cold-start phase of a Direct Injection Spark Ignition (DISI) engine is critical to meeting increasingly stringent emissions regulations. Computational Fluid Dynamics (CFD) modeling of gasoline DISI combustion under normal operating conditions has been discussed in detail using both the detailed chemistry approach and flamelet models (e.g. the G-Equation). However, there has been little discussion regarding the capability of the existing models to capture DISI combustion under cold-start conditions. Accurate predictions of cold-start behavior involves the efficient use of multiple models - spray modeling to capture the split injection strategies, models to capture the wall-film interactions, ignition modeling to capture the effects of retarded spark timings, combustion modeling to accurately capture the flame front propagation, and turbulence modeling to capture the effects of decaying turbulent kinetic energy. The retarded spark timing helps to generate high heat flux in the exhaust for the faster catalyst light-off during cold-start. However, the adverse effect is a reduced turbulent flame speed due to decaying turbulent kinetic energy. Accordingly, developing an understanding of the turbulence-chemistry interactions is imperative for accurate modeling of combustion under cold-start conditions. In the present work, combustion characteristics during the cold-start, fast-idle phase is modeled using the G-Equation flamelet model and the RANS turbulence model. The challenges associated with capturing the turbulent-chemistry interactions are explained by tracking the flame front travel along the Borghi-Peters regime diagram. In this study, a modified version of the G-Equation combustion model for capturing cold-start flame travel is presented.

Evaluation of pure rapeseed oil as a renewable fuel for agricultural machinery based on emission characteristics and long-term operation behaviour of a fleet of 18 tractors

The usage of locally produced pure rapeseed oil fuel (R100) according to fuel standard DIN 51605 in agricultural machinery can contribute to protecting the climate, water, and soil. Besides economic aspects, uncertainties concerning the long-term operation reliability and limited exhaust emissions of R100-operated agricultural machinery are hindering market entry. Thus, the aim of this research is to evaluate field experiences, such as downtimes and repairs, engine oil quality, and cold start behaviour, over a total period of more than 50,000 operation hours with 18 tractors. The tested tractors range from European Union exhaust gas stages I to IV and were configured for the use of R100. Additionally, performance, nitrogen oxides, and particulate matter were measured on a tractor test stand. The tractors demonstrated their full functionality under usual Bavarian farm conditions in daily use. Within the tractor fleet, no serious engine damage was observed, while minor malfunctions and necessary repairs occurred just occasionally. The operational reliability of the tested rapeseed-oil-fuelled tractors seemed to be comparable to that of diesel-fuelled tractors. The results of recurrent power and fuel consumption measurements gave no indication of engine deterioration. Furthermore, measurements proved that differences in exhaust gas emissions between R100 and diesel operation were marginal. Tractor models with exhaust gas after treatment systems were characterized by low emissions of nitrogen oxides and particulate matter in particular. With the 18 tractors running on R100, about 220 tonnes of CO2eq per year were saved on average from 2015 to 2017. It can be concluded that the usage of pure rapeseed oil fuel (R100) in compatible agricultural machinery is an implementable alternative to diesel fuel and can make an important contribution to reducing greenhouse gas emissions in agriculture. Nevertheless, there are some challenges to solve, particularly for modern agricultural machines with engines with exhaust gas aftertreatment systems.

Effects of Clamping Pressure on Cold Start Behavior of Polymer Electrolyte Fuel Cells

AbstractUnderstanding the cold start process of polymer electrolyte fuel cell (PEFC) is crucial to the development of an advanced PEFC of good cold start performance or to the design of advanced cold start strategies. In this study, a three‐dimensional cold start model has been adapted and further developed to numerically investigate the cold start behavior under the applied clamping pressure, which was not considered in previous cold start modeling and simulation work. The PEFC cold start performance is studied under various assembly pressures in terms of polarization curves, ice formation, water content profile, and current density distribution, etc. The results indicate that, using a large clamping pressure leads to a significant decline on the cold start performance; therefore, using an optimum clamping pressure is important to obtain a better cold start performance. It is found that increasing the clamping pressure not only increases the ice accumulation in cathode catalyst layer, but also causes the dehydration of membrane and decreases the cold start performance. The proposed model can be used as a powerful tool to study the realistic cold start performance of PEFC and to assist the development of more advanced PEFC cold start strategies.

On the water transport behavior and phase transition mechanisms in cold start operation of PEM fuel cell

An analytical dynamic model is proposed to predict the cold start behavior of proton exchange membrane (PEM) fuel cell. Water phase transition mechanisms have been reconstructed based on the five states of water migrating in the fuel cell, composed of water vapor, super-cooled water (liquid water), ice, membrane water (water dissolved in solid electrolyte) and frozen membrane water, in order to explore the reasonable water production and phase transition mechanism. The general water transfer behavior during cold start operation of PEM fuel cell finally evolves into four stages: (1) unsaturated water in ionomer and membrane water production; (2) water in ionomer reaching saturation; (3) over-saturated water in ionomer and quick desorption into liquid and vapor in pores; and (4) significant ice formation. Both non-equilibrium and equilibrium methods to simulate phase transition have been carried out to reveal water transport characteristics in the cold start operation. The assumptions associated with the liquid water and vapor production in the electrochemical reaction extensively involved in the previous modeling studies in the literature should be cautiously used, especially for the dynamic modeling studies. It is worthwhile addressing that the liquid water inside the cathode CL follows the slow increasing and rapid decreasing trend during the cold start operation, which indicates that the liquid water should mostly freeze at the shut-down moment. Furthermore, water prefers to freeze on the interface between catalyst layer (CL) and micro-porous layer (MPL), leading to the liquid water accumulation here migrating towards the membrane side.

Numerical investigation of cold-start behavior of polymer electrolyte fuel cells in the presence of super-cooled water

In this study, a mathematical model has been developed to simulate the transient cold-start processes of polymer electrolyte fuel cells. The super-cooled water is assumed to exist within the cell. The non-equilibrium water transfer between the membrane and the catalyst layer is considered. The models of water freezing and ice melting in the catalyst layer and gas diffusion layer have been established. For the first time, the randomicity of the freezing process is captured by introducing a freezing probability function. Based on this model, the cold-start processes of a single polymer electrolyte fuel cell starting at various operating and initial conditions have been simulated numerically. The results indicate that the cold-start performance of the cell is determined by the water storage potential of the electrolyte in cathode catalyst layer. For each startup temperature and operating current load, there is a most appropriate initial membrane water content, which corresponds to the longest cell shutdown time. When the cold-start process is failed, the ice is mainly accumulated in the cathode catalyst layer. The ice distribution becomes more non-uniform as the cold-start temperature is lower.

Experimental investigation on PEM fuel cell cold start behavior containing porous metal foam as cathode flow distributor

Metal foam has been regarded as one of the most important replacement for the conventional flow distributor of commercial fuel cells in recent years. One critical issue for the commercialization of proton exchange membrane (PEM) fuel cell is the successful startup from subzero temperatures. In this study, experimental tests on a PEM fuel cell using nickel metal foam as the cathode flow distributor are carried out to investigate the cold start performance. The cold start performance is also compared to a PEM fuel cell with parallel flow channels. Both galvanostatic and potentiostatic control are considered. The results show that under normal operating conditions the metal foam PEM fuel cell exhibits higher maximum net power density than the cell with parallel flow channels, whereas the parallel channel case exhibits slightly better performance at lower current densities. For cold start tests, metal foam is superior to the conventional parallel flow channel under galvanostatic control, due to its extremely porous structure, uniform mass and heat distribution. It is more difficult for PEM fuel cell under potentiostatic control to successfully start up due to possible ice blockage at the outlet.

Evaporation and Cold Start Behavior of Bio-Fuels in Non-Automotive Applications

Evaporation and Cold Start Behavior of Bio-Fuels in Non-Automotive Applications

A hybrid switching predictive controller with proportional integral derivative gains and GMDH neural representation of automotive engines for coldstart emission reductions

In this research, a high-performance predictive controller is developed for automotive coldstart emission reductions. The proposed control scheme combines a hybrid switching predictive controller (HSPC) with proportional integral derivative (PID) gains to simultaneously minimize the cumulative hydrocarbon emissions (HCcum) and the control input variations for a given engine during the coldstart operation. It is essential to use a sufficiently accurate surrogate meta-representation of the real engine within this model-based controller to predict the states of the plant and impart proper control commands to the system. The existing studies in the research literature have clearly demonstrated that automotive engines have a highly transient nonlinear behavior during coldstart periods and different disturbances can affect their operations. To cope with the mentioned difficulties, several coldstart experiments are performed to capture a comprehensive database for the considered engine. Thereafter, a powerful knowledge-based black-box meta-modeling tool, known as group method data handling (GMDH), is adopted to have a neural representation of the engine׳s coldstart behavior. As a real-time controller, the proposed PID-based HSPC requires a fast and robust solver to calculate the gains of PID in a computationally efficient manner. Here, a multivariate quadratic fit-sectioning algorithm (MQFSA) is proposed to deterministically determine the control commands. Other than the considered online optimizer, a powerful chaos-enhanced evolutionary algorithm (CEA) is used to heuristically optimize the prediction horizon (HP) and control commands horizon (HU) to achieve the best results. It is demonstrated that using such an optimizer, instead of trial-and-errors, to heuristically set the control and plant prediction horizon lengths is an effective strategy. Finally, several comparative studies are conducted to further indicate the efficacy of the proposed PID-based HSPC for the automotive coldstart control problem.

A rapid start-up strategy for polymer electrolyte fuel cells at subzero temperatures based on control of the operating current density

In a previous study, we numerically described the three distinct stages of ice evolution during the cold start of a polymer electrolyte fuel cell (PEFC), namely, the freezing, undersaturated, and melting stages. Based on our numerical observations, we propose an efficient start-up strategy for achieving a rapid cell temperature rise while simultaneously mitigating the rate of ice accumulation within a cell. The key to this cold-start strategy involves raising the operating current of the PEFC in the undersaturated stage, which accelerates the cell temperature rise without any further ice accumulation. Using a three-dimensional, transient cold-start model, we numerically demonstrate that raising the cell current in the undersaturated stage is very effective and significantly improves the cold-start behavior of a PEFC. In contrast, increasing the cell current in the freezing stage has a negative impact on the PEFC cold start in that the oxygen reduction reaction causes the water production rate to increase, leading to more rapid ice growth. This ultimately results in cold-start failure and the deterioration of the porous electrode structure. This study clearly illustrates that optimization of the cold-start operation is key to improving the cold-start performance, while also pointing to the importance of the roles played by PEFC cold-start modeling and the simulations used to search for an optimum cold-start strategy.

Effects of porous properties on cold-start behavior of polymer electrolyte fuel cells from sub-zero to normal operating temperatures.

In this investigation, a parametric study was performed using the transient cold-start model presented in our previous paper, in which the ice melting process and additional constitutive relations were newly included for transient cold-start simulations of polymer electrolyte fuel cells (PEFCs) from a sub-zero temperature (−20°C) to a normal operating temperature (80°C). The focus is placed on exploring the transient cold-start behavior of a PEFC for different porous properties of the catalyst layer (CL) and gas diffusion layer (GDL). This work elucidates the detailed effects of these properties on key cold-start phenomena such as ice freezing/melting and membrane hydration/dehydration processes. In particular, the simulation results highlight that designing a cathode CL with a high ionomer fraction helps to retard the rate of ice growth whereas a high ionomer fraction in the anode CL is not effective to mitigate the anode dry-out and membrane dehydration issues during PEFC cold-start.