Cold Start Conditions Research Articles

Numerical study of plasma produced ozone assisted combustion in a direct injection spark ignition methanol engine

Numerical simulations were performed to better assess the effect of plasma produced ozone assisted combustion. The effects of ozone (O3) addition from 0 to 7000 ppm in the intake manifold on cylinder pressure history, ignition delay, cylinder temperature history, and formaldehyde unburned methanol emission of a direct injection spark ignition (DISI) methanol engine during cold start and steady state conditions were simulated using computational fluid dynamics to couple the methanol chemical and kinetics reaction mechanisms. The model results show that the maximum cylinder pressure increases with increasing O3 addition for cold start and steady state modes. O3 addition can also significantly reduce ignition delay. Two maximum heat release rate peaks occurred with O3 addition for cold start and steady state modes. The effect of O3 addition on combustion processes of DISI methanol engines was significantly greater for cold start than steady state mode, particularly with higher O3 concentrations. The effects on formation and oxidation of formaldehyde were greater than for unburned methanol, and the effects on formation and oxidation of formaldehyde were also significantly greater for cold start than steady state mode.

An investigation for reducing combustion instability under cold-start condition of a direct injection gasoline engine

In order to meet recent stringent emission regulations, the exhaust catalyst should be heated as early as possible to activate the purifying reactions. In a direct injection spark-ignition engine, a combination of late fuel injection during the compression stroke and late ignition in the expansion stroke is a common strategy to quickly raise exhaust gas temperature for subsequent rapid activation of exhaust catalysts. However, this approach under cold start-up of an engine often results in incomplete and unstable combustion. In this study, to explore the conditions of stable ignition and combustion, the effect of injection timing on indicated mean effective pressure and early combustion duration (MBD0.5) are first investigated by an analysis of the pressure indicator diagram. As this analysis shows a strong correlation between indicated mean effective pressure and MBD0.5, the mechanism of initial flame propagation is investigated intensively using optical diagnostics. Namely, mean equivalence ratio of mixtures in the propagating flame front is measured by focusing on the ratio of C2* to CH* emission intensities. The flow velocity and turbulence intensity around the spark electrode are measured by the back-scattering laser Doppler anemometry. Two major conclusions are derived from this study: First, when the injection timing is retarded, the mean equivalence ratio increases as the time for the injected fuel to travel and diffuse is shortened. The most preferable mean equivalence ratio for fast initial combustion is found to lie in a range from 1.2 to 1.4. Second, when the second injection timing is retarded further, the mean equivalence ratio increases exceeding 1.4, and this results in slower and more fluctuated initial flame propagation. But, if the turbulent intensity is increased by means of the spray induced air motion, the slowed initial combustion can be recovered.

Applying forward dynamic programming to combined energy and thermal management optimization of hybrid electric vehicles

The efficiency of internal combustion engines (ICEs) is well-known to be low at cold starting conditions. Additionally, the energy demand for passenger compartment heating is substantial and either provided by an electrical auxiliary heater or in terms of the engine waste heat. Plug-in hybrid electric vehicles (PHEVs) are prone to suffer from extended warm-up periods due to increased engine off periods as compared to conventional vehicles. Energy management strategies (EMSs) however allow for warm-up applications independent of the drive torque request. Optimal control theory serves as benchmark for EMS, offering a variety of numerical methods. This paper focuses on forward dynamic programming (FDP) accounting for causal system dynamics such as engine temperature. Results confirm, that even though the fuel saving potential of the engine warm-up is significant, it is hardly influenced by means of the EMS. A second implementation variant is proposed to counteract the curse of dimensionality. The presented approach not entirely achieves global optimality, yet yields results close to optimum within reasonable computational times. As opposed to the reference, the proposed method allows accounting for a variety of causal system dynamics leading towards an EMS more close to reality.

A Physics-Based Three-Way Catalytic Converter Model for Real-Time Prediction of Temperature Distribution

Thermal management of aftertreatment devices is a critical requirement to comply with the stringent emission standards. A recent challenge in aftertreatment control and diagnostics is the need to monitor the temperature distribution along the entire length of the catalyst, rather than relying on a single-point measurement. To this extent, this work focuses on the preliminary development of a control-oriented, physics-based Three-way Catalytic Converter (TWC) model for the purpose of real-time thermal monitoring. Starting from the governing equations for the TWC thermal model in Partial Differential Equation (PDE) form, a model order reduction technique that combines Proper Orthogonal Decomposition and Collocation is proposed. The reduced order model executes much faster than using standard numerical methods, and meanwhile provides comparable accuracy. The model is also validated against GT-Power in the ability to predict the temperature distribution during cold-start conditions.

A study of particulate matter emissions from a DI gasoline engine at cold start and warming-up conditions

A study of particulate matter emissions from a DI gasoline engine at cold start and warming-up conditions

Enhanced oxidation of naphthalene using plasma activation of TiO2/diatomite catalyst

Non-thermal plasma technology has great potential in reducing polycyclic aromatic hydrocarbons (PAHs) emission. But in plasma-alone process, various undesired by-products are produced, which causes secondary pollutions. Here, a dielectric barrier discharge (DBD) reactor has been developed for the oxidation of naphthalene over a TiO2/diatomite catalyst at low temperature. In comparison to plasma-alone process, the combination of plasma and TiO2/diatomite catalyst significantly enhanced naphthalene conversion (up to 40%) and COx selectivity (up to 92%), and substantially reduced the formation of aerosol (up to 90%) and secondary volatile organic compounds (up to near 100%). The mechanistic study suggested that the presence of the TiO2/diatomite catalyst intensified the electron energy in the DBD. Meantime, the energized electrons generated in the discharge activated TiO2, while the presence of ozone enhanced the activity of the TiO2/diatomite catalyst. This plasma-catalyst interaction led to the synergetic effect resulting from the combination of plasma and TiO2/diatomite catalyst, consequently enhanced the oxidation of naphthalene. Importantly, we have demonstrated the effectiveness of plasma to activate the photocatalyst for the deep oxidation of PAH without external heating, which is potentially valuable in the development of cost-effective gas cleaning process for the removal of PAHs in vehicle applications during cold start conditions.

Experimental study on combustion and emission characteristics of turbocharged gasoline direct injection (GDI) engine under cold start new European driving cycle (NEDC)

In this study, the combustion and emission characteristics of a turbocharged GDI engine under cold start NEDC were investigated based on chassis dynamometer test. The operating states, combustion and emission performance of GDI engine were measured continuously during vehicle driving cycles. Then, the combustion and emission characteristics of GDI engine under cold start NEDC were obtained and the influence factors were revealed by synchronous analysis of various operating parameters. The results show that, the combustion duration from start of combustion (SOC) to 50% combustion location changes a little under cold start NEDC. At most time, the 10–90% combustion duration usually changes in the range of 20–40 °CA, which turns longer under idling conditions but shorter under acceleration conditions. Since the sparking timing is severely retarded in the beginning stages of NEDC, the effect of cold start on hydrocarbon (HC) emission is very limited. HC emission increases sharply under deceleration conditions, due to the decrease of engine indicated mean effective pressure (IMEP). Carbon monoxide (CO) emission does not seem to have relevance to the cold start condition, and it is very sensitive to excess air coefficient while the effects of other parameters are very little. Nitrogen oxide (NOx) emission increases under acceleration conditions but decreases under deceleration conditions, which is mainly influenced by the IMEP, then followed by engine speed. All those not only demonstrated the change rules of combustion and emission characteristics of turbocharged GDI engine under cold start NEDC, but also provided the guidance for improving the vehicle emission performance.

Ignition-Characteristic Research of the Diesel Fuel in Combustion Vessel Simulated Diesel Engine Cold Start Condition

AbstractThe initial ignition characteristic of fuel spray in a diesel engine is of great significance in the cold start problem. In this paper, the constant volume combustion vessel was applied to ...

Thermophysical properties of rapeseed oil methyl esters (RME) at high pressures and various temperatures evaluated by ultrasonic methods

Investigation of the high-pressure thermophysical properties of biofuels, e.g., bulk modulus, surface tension, and viscosity is of paramount importance in fuel injection systems in diesel engines. Another crucial and dangerous phenomenon that may occur in biofuels at high pressures is phase transition (solidification), which can drastically increase the viscosity of the biofuel. This effect may hamper proper operation of the engine, especially under cold-start conditions. Unfortunately, the availability of high-pressure thermophysical properties of biofuels is still limited. The goal of this paper is to investigate the impact of high pressures on thermophysical properties of biofuels on the example of rapeseed fatty acid methyl esters (RME) in a wide range of pressures (0.1to250MPa) and temperatures (5to20°C). To this end we employed innovative ultrasonic techniques, i.e., the Bleustein-Gulyaev surface acoustic waves for measuring RME viscosity, and ultrasonic bulk compressional waves for measuring sound velocity in RME and consequently evaluating RME thermophysical parameters, e.g., bulk modulus and surface tension. The viscosity of the measured RME displayed an abrupt increase at pressures: 260 MPa (t=20°C), 230 MPa (t=15°C), 190 MPa (t=10°C), and 130 MPa (t=5°C). Evidently it was a signature of the phase transition (solidification) occurring in the RME. The discovered high viscosity high-pressure phase in RME can be very detrimental for operation of modern common rail Diesel engines. Therefore, the results of research presented in this paper should be interesting for engineers and designers working with modern common rail Diesel engines using biofuels.

Influence of flash boiling spray on the combustion characteristics of a spark-ignition direct-injection optical engine under cold start

Flash boiling occurs when liquid fuel is injected into an ambient environment below its saturation pressure. Compared to non-flash-boiling (liquid) spray, flash-boiling spray features a two-phase flow that constantly generates vapor bubbles inside the liquid spray thus results in much smaller drop size and faster evaporation, which are favorable for direct-injection gasoline engine combustion. In this study, the combustion characteristics of flash boiling spray was investigated under cold start condition in a spark-ignition direct-injection (SIDI) optical gasoline engine. Three spray conditions, including liquid, transitional flash boiling, and flare flash boiling spray were studied for comparison. Optical access into the combustion chamber was realized by a quartz insert on the piston. The crank angle resolved color flame images as well as in-cylinder pressure of 150 consecutive cycles were recorded simultaneously. From the color images, the blue flame generated by excited molecules and the yellow flame resulted from soot radiation was identified and analyzed separately alongside with the cylinder pressure. Results show an improvement of indicated mean effective pressure-gross (IMEPg) and a reduction of soot formation with the introduction of flash boiling spray under cold start condition. The emission measurement shows that the formation of soot is positively related to particulate number (PN) emissions. Further study on the transient development of in-cylinder flames shows that flash boiling spray leads to higher propagation rate of the blue flame, and a subsequent statistical analysis shows a positive correlation between IMEP and the propagation rate of the blue flame.

ISelf

It has been a consensus that a certain relationship exists between personal emotions and usage pattern of the smartphone. Based on users’ emotions and personalities, more and more applications are developed to provide intelligent automation services on the smartphone, such as music recommendations or stranger introductions on social networking sites. Most existing work studies this relationship by learning large amounts of samples, which are manually labeled and collected from smartphone users. The manual labeling process, however, is very time-consuming and labor-intensive. To address this issue, we propose iSelf, a system that provides a general service of automatic detection of a user’s emotions in cold-start conditions with a smartphone. With the technology of transfer learning, iSelf achieves high accuracy given only a few labeled samples. We also embed a hybrid public/personal inference engine and validation system into iSelf, to make it maintain updates continuously. Through extensive experiments in real traces, the inferring accuracy is tested above 74% and can be improved increasingly through validation and updates. The application program interface has been open online for other developers.

Effect of electrically heated catalytic converter on emission characteristic of a motorcycle engine in cold-start conditions: CFD simulation and kinetic study

Emissions from motorcycles are well known to be a serious cause of environmental pollution. One of the most effective ways to reduce the emissions during cold start of the motorcycle engine is using electrically heated catalytic converters (EHC). In this study, a kinetic model has been developed by using CFD methods to investigate the effects of using EHC on CO emission from motorcycle engines. Apart from three different heating temperatures (600, 800 and 1000K), the other studied parameters included the heating position (the inlet and the mid-section of the catalyst converter) and heating duration (20, 25 and 35s). Results showed that using the heater at the inlet of the catalytic converter is more effective than when it is in mid-section and the converter has a higher reaction performance. Moreover, the results indicated that the minimum heating temperature which required the converter to reach the light-off point is 450K. In addition, the results revealed that when the heaters were turned on prior to cold starting the engine for duration of 35s, the higher CO conversion occurs.

The formation and evolution of the core-corona structure in the electrical explosion of aluminum wire in vacuum: experimental and numerical investigations

Experimental and numerical investigations on the formation and evolution of the core-corona structure in the electrical explosion of aluminum wire in vacuum are presented. In the experiments of aluminum wire explosion, shadowgraphy, interferometry and schlieren optical diagnostics are constructed with a laser probe to study the morphological evolution and distribution of the core and corona. A set of computational models with cold start conditions, consisting of a thermodynamic calculation and magnetohydrodynamic model combined with a semi-empirical equation of state and transport coefficients, are established to reproduce the behavior of the electrical explosion of aluminum wire. The radial profiles of the density, temperature, current density and magnetic field, addressing the physical scenario of the formation and evolution of the core-corona structure are analyzed. The numerical results are also compared with relevant experimental data.

Spacecraft orbit propagator integration with GNSS in a simulated scenario

When space vehicles operate above the Global Navigation Satellite System (GNSS) constellation or even above geosynchronous orbit, it is common that the traditional GNSS single–epoch solution can’t meet the requirement of orbit determination (OD). To provide the required OD accuracy continuously, a new designed spacecraft orbit propagator (OP) is combined with the GNSS observations in a deep integration mode. Taking both the computational complexity and positioning accuracy into consideration, the orbit propagator is optimized based on a simplified fourth order Runge-Kutta integral aided with empirical acceleration model. A simulation scenario containing a typical Highly-inclined Elliptical Orbit (HEO) user and GPS constellation is established on a HwaCreat™ GNSS signal simulator to testify the performance of the design. The numerical test results show that the maximum propagation error of the optimized orbit propagator does not exceed 1000m within a day, which is superior to conventional OPs. If the new OP is deeply integrated with GNSS in our proposed scheme, the 95% SEP for the OD accuracy is 10.0005m, and the time to first fix (TTFF) values under cold and warm start conditions are reduced by at least 7s and 2s respectively, which proves its advantage over loose integration and tight integration.

A study of the tribological impact of biodiesel dilution on engine lubricant properties

The switch from petro-diesel fuel to biodiesel blends for Compression Ignition engines have raised tribological performance concerns among major automobile manufacturers. Biodiesel dilution on engine lubricants could have adverse long-term effects on the engine efficiency, which will reduce the fuel economy, thus, leading to higher greenhouse gas emissions. Therefore, this study investigates the tribological impact of palm methyl ester (PME) diluted in SAE5W40 and SAE10W40 engine lubricants along different lubrication regimes under engine cold start condition. Through lubrication Stribeck curve analysis conducted using a pin-on-disc tribometer, coefficient of friction (CoF) for both engine lubricants showed parabolic maximum behaviour with increasing PME dilution. The CoF reduction beyond these peak values is attributed to the improved friction modifier effect from the now-dominant PME but with reduced load carrying capacity. An effective lubricant should possess both reasonable friction modifier effect and highest load carrying capacity in mitigating boundary friction. Hence, through the study, it could be deduced that the acceptable PME dilution threshold level for SAE5W40 is up to 17.5-vol%, while for SAE10W40 is between 28.0-vol% and 34.5-vol%. PME dilution levels beyond these thresholds could easily cause lubrication film rupture under high load, high shear rate conditions during application along the mixed to boundary lubrication regimes, inducing material wear.

Transient emission characteristics of a heavy-duty natural gas engine at stoichiometric operation with EGR and TWC

The recent issued emission regulations have more stringent standards for the transient emissions of natural gas engines. When equipped with cooled exhaust gas recirculation (EGR) and three way catalyst (TWC), natural gas engines operating at stoichiometric conditions are capable of achieving extremely low transient emissions. In this paper, the transient emission characteristics of a heavy-duty natural gas engine at stoichiometric operation with EGR and TWC are experimentally studied based on the world harmonized transient cycle (WHTC). The results show that both the raw carbon monoxide (CO) and total hydrocarbon (THC) emissions are higher in the hot start test while the raw NOx emissions are higher in the cold start test. When measurements are conducted after the TWC, all these emissions are higher in the cold start test. Among all the sub-cycles of WHTC, the urban sub-cycle plays the most important role for all three emissions in both cold start and hot start conditions except the after three way catalyst (ATWC) CO emissions in the cold start test, where the motorway sub-cycle takes up the highest percentage. In summary, CO, nitrogen oxide (NOx) as well as non-methane hydrocarbon (NMHC) emissions can meet the requirements of Euro VI emission standards, whereas CH4 emissions are higher than the corresponding standard, suggesting that improvements in the performance of the catalyst are essential.

The impact of starting process on wear of cylinder wall

The results of experimental research of cylinder wall wearing process were presented in this article. Researches were conducted onthe basis of four strokes spark ignition one cylinder engine. The main goal of presented research was assessment of impact of cold start condition on intensity of cylinder wall wearing process. The new one and worn engine oil with grade 10W40 was used for experimental research. The experimental research was conducted on specially developed experimental stand. The wear of cylinder wall was assessed on the basis of cylinder diameter and wall roughness measurements.

An investigation on a diesel jet’s ignition characteristics under cold-start conditions

The diesel engine is widely regarded as a critical power source for transportation vehicles, construction machinery vehicles, and military-equipment due to its advantages of significant horse power, higher fuel efficiency, greater reliability. However, diesel engines do suffer from ignition issues in extremely cold environments. Ignition characteristics during the start-up process directly impact both the start-ability and emission levels of the diesel engine. In this study, various optical diagnostics, such as Mie scattering, shadowgraphy method, and high-speed imaging, were applied to investigate the spray’s vapor and liquid phases as well as the initial flame development, while an optical constant volume chamber was used to observe the in-cylinder condition. During the experiments, the ambient temperature, injection pressure, and fuel temperature was varied in a large range to simulate different stages of the cold-start or warm-up processes. The results show that the penetration of the spray’s liquid and vapor phases, flame lift-off length, and ignition delay all observably increase with a decrease in the ambient density, ambient temperature, and fuel temperature. Furthermore, the chemical process is the dominant factor for ignition at a low ambient temperature. A low ambient temperature may lead to a misfire due to the separation between the spray’s vapor phase and the expected initial flame location. Additionally, a low ambient density could lead to misfires due to the low heating capacity of the ambient gas. The study results also show that the injection pressure does not significantly influence the ignition delay or the flame lift-off length, but a higher pressure could result in a lower ignition success rate due to over-mixing of the air-fuel. Additionally, the fuel temperature significantly influences the ignition, which advances the initial ignition time 0.1ms with every increase of 10°C under an ambient temperature of 535°C.

Numerical study of formaldehyde and unburned methanol emissions of direct injection spark ignition methanol engine under cold start and steady state operating conditions

The effects of overall equivalence ratio, injection timing, and ignition timing on formaldehyde and unburned methanol emissions, cylinder temperature histories, and formaldehyde emission histories of a spark ignition direct injection stratified charge methanol engine during cold start and steady state conditions were simulated using computational fluid dynamics coupling the methanol chemical kinetics reaction mechanism. The model results show that the overall equivalence ratio is less than 0.43, and unburned methanol significantly higher for cold start mode. For steady state mode, when the overall equivalence ratio is less than 0.4, formaldehyde and unburned methanol emissions increase rapidly. When the overall equivalence ratio is larger than 0.4, formaldehyde and unburned methanol emissions are very low. Formaldehyde and unburned methanol emissions for steady state mode are significantly lower than for cold start mode. For steady state mode at engine speed 1600rpm and brake mean effective pressure 0.67MPa formaldehyde and unburned methanol emissions are reduced 90% and 98%, respectively, compared to cold start mode at the same overall equivalence ratio (0.5). Cylinder temperature is the main factor that affects formaldehyde generation and consumption. There is a rapid decrease due to oxidation at the corresponding position of the maximum cylinder temperature, after which formaldehyde is quickly generated for any operating conditions.

Experimental Study on the Emission and Particle Number of a Heavy-duty Gasoline Vehicle by the Heavy-duty Chassis-Dynamometer

This paper uses the AVL company's emissions sampling and analysis equipment to take the vehicle emission test with a heavy-duty gasoline vehicle on one chassis dynamometer. And then have an analysis and compare on the PN and the polluted gas (CO, THC, NOx) during different start test cycles. And this study shows that the cold start condition has higher particulate number and more gaseous pollutants than hot start condition, the particulate number was concentrated in different drive conditions during different starting conditions, and it is close to the sudden acceleration.