Browse Topic: Starters and starting
Current lithium-ion batteries should generally only be charged above 0 °C, as charging below this temperature can promote lithium plating and irreversible degradation. However, conventional pack-level heating elements increase system mass and design complexity. In addition, heat is transferred from outside into the cell, causing the temperature inside the cell to rise slowly. This study evaluates internal Joule heating of cylindrical Li-ion cells using a zero-mean square-wave current excitation and quantifies the associated aging impact. LG INR21700-M50L cells were tested at 0 °C, −10 °C, and −20 °C with three excitation frequencies (50 Hz, 1 Hz, 10 mHz) at 5 A amplitude. Each cycle consisted of 30 min heating followed by 60 min cooling; reference capacity-based state of health (SOH) was assessed every 50 cycles up to 400 cycles. A maximum surface temperature rise of 14.3 K was achieved, with larger temperature rise at lower ambient temperature and lower excitation frequency. Capacity fade remained below approximately 1% for most conditions; however, at −20 °C and 10 mHz a pronounced SOH decrease to 87% was observed, indicating a critical operating regime. The results provide practical guidance for pulse-heating parameter selection and highlight the need for safeguards and further diagnostics in extreme low-frequency excitation at very low temperatures. This heating approach is particularly suitable for simpler battery-electric applications without thermal management, such as e-bikes or power tools. However, it may also be relevant for applications with existing thermal management systems, as it simplifies battery pack design.
Hybrid electric vehicles (HEVs) with an increasing level of electrification, are becoming a major part of the global energy transition. To achieve lower engine tailpipe exhaust emissions and improve total fuel consumption, typically the HEV control system expertly and frequently switches between the internal combustion engine and electric motor drive, with multiple stops and restarts of the internal combustion engine (ICE). As a consequential result of this switching, are typically slower or even incomplete engine warm-up times, depending on the engine speed, load pattern and run time of the vehicle drive cycle. Along with the speed and load transient control, the engine stop and start processes are also challenging to control, with respect to cold start fuel and combustion by-products entering the oil. Consequently, contamination enters the engine oil but may not completely leave. These effects are highly transient over the drive cycle. Contaminants and in particular, fuel dilution, will affect the engine oil viscosity. To demonstrate this whilst yielding insights, a precisely controlled engine test cell, running the cold start Worldwide Harmonized Light Duty Transient Cycle (WLTC) for both, a non-hybridized ICE only vehicle and a HEV in charge sustaining mode operation is described. This also has on-line viscosity sensing and oil sampling. Typical data is shared along with engine oil comparisons. For complimentary insights, the impact of the fuel dilution on engine friction was investigated using a novel, precise, fully transient engine friction test rig, which measures gasoline direct injection high pressure fuel-pump friction and engine oil viscosity accurately. The cycle is based on measured data from vehicles tested on a chassis dynamometer. On-line friction data, with oil comparisons is used to show real-time data of the effect of fuel dilution on the frictional energy required, thus CO2 over the full WLTC.
This paper is to introduce a new catalyst family in gasoline aftertreatment. The very well-known three-way catalysts effectively reduce the main emission components resulting from the combustion process in the engine, namely THC, CO, and NOx. The reduction of these harmful emissions is the main goal of emission legislation such as Bharat VI to increase air quality significantly, especially in urban areas. Indeed, it has been shown that under certain operating conditions, three-way catalysts may produce toxic NH3 and the greenhouse gas N2O, which are both very unwanted emissions. In a self-committed approach, OEMs could want to minimize these noxious pollutants, especially if this can be done with no architecture change, namely without additional underfloor catalyst. In most Bharat VI gasoline aftertreatment system architectures, significant amounts of NH3 occur in two phases of vehicle driving: situations with the catalyst temperature below light-off, which appear after cold start or at low-speed urban driving and hot, high mass flow phases. In this paper, we will compare several approaches to reduce NH3 starting with an existing gasoline technology, diesel technologies modified to gasoline conditions and the especially developed novel gasoline Secondary Emission Treatment (SET) catalyst, providing both ammonia abatement and underfloor three-way functionality. SET is the combination addressing both the cold start phase and hot driving conditions. In addition, it fulfills the role of an underfloor three-way catalyst, responsible for CO and NOx hot phase treatment.
A cold start occurs when the engine is cranked after being off for a long time, enough for its temperature to drop down to the cold ambient levels. Cold start in an engine is a critical phase as it is characterized by elevated emissions. During a cold start, exhaust components such as catalytic converter do not operate in its optimal temperature zone leading to reduced efficiency in emission control. New regulations for engine emissions are becoming stringent for this condition, hence it is important to accurately determine cold start condition in an engine to optimize the emissions control strategy. Accurate engine off time calculation plays a crucial role in cold start detection, emissions control and On-Board Diagnostics (OBD-II) decision making. This engine off time if greater than 6 hours indicates one of the conditions to confirm a cold start. Other conditions such as Ambient temperature and coolant temperature along with the engine off time confirms a cold start. This paper presents a novel approach to calculate engine off time without any need for supplementary new hardware, leveraging detection of cold start to meet the new requirements for Cold start emission reduction strategy (CSERS) for OBD-II diagnostics. The proposed methodology utilizes Real time clock to estimate the time difference between a successful Engine Cranking and previous engine off to accurately estimate engine off time, enabling precise differentiation between a cold and a warm start.
Hydrogen internal combustion engines (H2-ICE) do not emit any fuel-borne carbon emission species. Nitrogen oxides are the remaining raw emission species at significant levels. However, the exhaust aftertreatment system is exposed to a different exhaust matrix, including unburned hydrogen. This raises the question of the role of hydrogen emissions for the aftertreatment system. Extensive synthetic gas bench (SGB) test campaigns address the role of hydrogen in several production catalyst components. Starting with selective catalytic reduction (SCR) systems, a systematic variation of the hydrogen concentration shows rather small effects on the NOX reduction performance. A change in selectivity results in increased secondary N2O emissions for a copper-zeolite system, whereas a vanadium-based SCR catalyst is unaffected. However, both SCR types are highly sensitive to the NO2/NOX ratio in the raw emission. Therefore, an upstream oxidation catalyst remains important for low temperature performance. Investigations of oxidation catalysts with varying platinum loadings show increased oxidation performance with higher hydrogen content. This effect is attributed to the accelerated heating of the catalytic centers due to the exothermic hydrogen reaction. In parallel however, secondary N2O emissions increase during light-off, speaking against a post-oxidation-based catalyst heating strategy. The strongest sensitivity to hydrogen is found in lambda sensors. Fast hydrogen diffusion through the zirconia distorts the signal towards rich mixtures. Overall, the results emphasize the important role of hydrogen, especially with respect to secondary N2O emissions, requesting H2-ICE-specific operating strategies to achieve zero-impact tailpipe emissions.
Opening a tailgate can cause rain that has settled on its surfaces to run off onto the customer or into the rear loadspace, causing annoyance. Relatively small adjustments to tailgate seals and encapsulation can effectively mitigate these effects. However, these failure modes tend to be discovered relatively late in the design process as they, to date, need a representative physical system to test – including ensuring that any materials used on the surface flow paths elicit the same liquid flow behaviours (i.e. contact angles and velocity) as would be seen on the production vehicle surfaces. In this work we describe the development and validation of an early-stage simulation approach using a Smoothed Particle Hydrodynamics code (PreonLab). This includes its calibration against fundamental experiments to provide models for the flow of water over automotive surfaces and their subsequent application to a tailgate system simulation which includes fully detailed surrounding vehicle geometry. This approach simulates the accumulation of rain on the rear surfaces of a stationary vehicle over the course of 60 s, which is followed by a drainage period of 20 s (rain source off). Once the starting conditions have been set, the simulation captures the dynamics of the tailgate opening and subsequent surface water run-off. This enables the mechanisms of run-off into the rear loadspace to be explored. Further, we also show the effect of a small modification to the tailgate encapsulation, demonstrating, by reference to physical test, that this simulation method can accurately replicate both the failure mode and its mitigation.
In cost- effective P2 hybrid vehicles with low voltage electric machines connected to the engine, an interesting control problem arises during the transition to a locked driveline state. This occurs when the engine connects to the wheels via a separation clutch. The two primary torque sources, the engine and the clutch, are traditionally imperfect estimators of applied and transferred torques. The Hybrid Supervisor’s feedforward constraints model relies on these imperfect inputs to determine torque and acceleration limits for the engine’s desired acceleration profiles and to specify engine feedforward commands, aiming for synchronization speed. Due to the inaccuracies in the torque estimates of the engine and clutch, the Hybrid Supervisor is susceptible to control windup, increased jerk to the driveline during synchronization, and inaccurate computation of its target acceleration profile, speed, and torque targets for the engine to achieve synchronization speed. This paper presents a disturbance estimation strategy to minimize control windup in the development of the Hybrid Supervisor’s speed trajectory, engine feedforward torque commands, and acceleration commands for transitioning a low voltage P2 Hybrid from EV Mode to Hybrid Mode. Simulation and vehicle results indicating the profiled engine speed remains within +- 5 to 8% of its target with minimal overshoot till we get to synch speed, are provided to demonstrate the strategy’s effectiveness.
As the global energy transition moves to increased levels of electrification for passenger cars, then the number and role of hybrid electric vehicles (HEVs) increases rapidly. For these, the power reaches the road from an internal combustion engine (ICE) and/or an electric motor, with several switches between these three modes, over a typical drive-cycle. Consequently, this comes with a large increase in the number of significant engine stop and start events. Such events are potentially challenging for the HEV engine lubricant, as by comparison, for standard ICE cycles there is almost continuous relative movement of the two lubricated surfaces, for most areas of the engine. Based on both field and test cell observations, a challenging area for the lubricant within the gasoline direct injection (GDI) engine is the high pressure (HP) fuel pump, typically driven by a cam and follower, whilst lubricated by engine oil. From engine start, the speeds are low, also the fuel pump loads are high and transient. The loads continue to be variable and highly transient over a drive-cycle. A novel motoring friction test rig is described, which measures transient GDI HP fuel pump friction accurately. Using the same engine, further comparison data showing the contribution of this to engine friction is presented over the Worldwide Harmonized Light Duty Transient Cycle (WLTC), for both ICE and two types of HEV operating in charge sustaining mode (CS mode); lubricant friction differentiation in this area is shown. Based on measured data from vehicles tested on a chassis dynamometer, this friction rig runs from a controlled cold start, whilst also achieving the correct transient oil and coolant warm-up profiles. Further, it achieves the vehicle highly transient fuel flow, so the relevant transient GDI pump cam loading, over the WLTC. The frictional energy required is used to compare engine lubricants.
Battery cell aging and loss of capacity are some of the many challenges facing the widespread implementation of electrification in mobility. One of the factors contributing to cell aging is the dissimilarities of individual cells connected in a module. This paper reports the results of several aging experiments using a mini-module consisting of seven 5 Ah 21700 lithium-ion battery cells connected in parallel. The aging cycle comprised a constant current-constant voltage charge cycle at a 0.7C C-rate, followed by a 0.2C constant current discharge, spanning the useful voltage range from minimum to maximum according to the cell manufacturer. Charge and discharge events were separated by one-hour rest periods and were repeated for four weeks. Weekly reference performance tests were executed to measure static capacity, pulse power capability and resistance at different states of charge. All diagnostics were normalized with respect to their starting numbers to achieve a percentage change over time. Both electrical and thermal dissimilarities were considered by initial cell selection or adjusting the thermal boundary conditions, respectively. The latter was achieved by contrasting air cooling with direct liquid immersion cooling which prevented temperature spikes and ensured more uniform temperature distribution between the cells. For well-clustered cells, the use of immersion cooling reduced the capacity fade noticeably when compared to air cooling. However, when cells are not well clustered, the impact of electrical dissimilarities overshadowed the thermal benefits. Poor cell clustering resulted in a lower discharge resistance increase which itself reflected as smaller changes of the pulse power fade. The results highlighted the importance of cell selection and clustering during research and when building packs for final application and reinforced the benefits of good thermal management. The work did not fully explore the benefits of immersion cooling due to the moderate C-rates used.
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