Development of an Ammonia Reduction After-Treatment Systems for Stoichiometric Natural Gas Engines

Three-way catalyst (TWC) equipped stoichiometric natural gas vehicles have proven to be an effective alternative fuel strategy that shows significant low NOx emissions characteristics. However, recent studies have shown the TWC activity to contribute to elevated levels of tailpipe ammonia (NH 3) emissions. Although a non-regulated pollutant, ammonia is a potent pre-cursor to ambient secondary PM formation. Ammonia is an inevitable byproduct of fuel rich operation that results in lowest NOx slip through the TWC after-treatment system.;The main objective of the study is to develop a passive Ammonia Reduction Catalyst (passive-ARC) based NH3 reduction strategy that results in an overall reduction of ammonia as well as NOx emissions. The study investigated the characteristics of Fe-based and Cu-based zeolites SCR catalysts in storage and desorption of ammonia at high exhaust temperature conditions, that are typical of stoichiometric natural gas engines. Continuous measurements of NOx and NH3 before and after the SCR systems were conducted using a Fourier Transform Infrared Spectrometry (FTIR) gas analyzer. Results of the investigation showed that both, the Fe- and Cu zeolite SCRs adsorbed above 90% of TWC generated NH3 emissions below 350--375 °C SCR temperatures. Desorption or slipping of NH3 was observed at exhaust gas temperatures exceeding 400 °C. In terms of NOx conversions, Fe-zeolite showed efficiency between 50--80% above temperatures of 300--350 °C while Cu-zeolite performed well at lower SCR temperature from 250 °C and above with a conversion efficiency of greater than 50%.;In order to efficiently reduce both NOx and NH3 simultaneously over longer durations it was found that an engine-based air fuel ratio operation strategy for the passive-ARC system must be developed. To this extent, the study extended its objectives to develop an engine-based control strategy that results in stoichiometric ammonia production operation followed by brief lean operation to regenerate the saturated ammonia reduction catalyst using high NOx slip through TWC. The study presents comprehensive results of ammonia storage characteristics of SCRs pertaining to stoichiometric natural gas engine exhaust as well as an advanced engine control strategy approach to simultaneously reduce both NOx and NH3 using an alternating air -fuel ratio approach

Optimisation of autoselective plasma regeneration of wall-flow diesel particulate filters

The increase in number of diesel powered vehicles has led to greater concern for the effects of their exhaust emissions. Engine manufacturers must now consider using diesel particulate filters to make their engines meet the legislated limits. Diesel particulate filters can remove more than 95% of the particulates from the exhaust flow but require cleaning, known as regeneration. This thesis describes the research and optimisation of the Autoselective regeneration system for cordierite wall flow diesel particulate filters. The novel Autoselective technology uses an atmospheric pressure glow discharge plasma to selectively oxidise particulate matter (soot) trapped within the filter. The aim of this research was to produce a regeneration system that can operate under all exhaust conditions with a low energy demand and no precious metal dependence to compete with the numerous pre-existing technologies. The effect of discharge electrode type and position on regeneration performance has been investigated in terms of regeneration uniformity, power requirement and regeneration rate. The results showed that the electrode orientation had a large effect on regeneration distribution and energy demand. The electrode capacitance and breakdown voltage was shown to affect the choice of power supply circuit because not all power supply topologies were suitable for powering electrodes with >100 pF capacitance. A number of power supplies were designed and tested, a voltage driven resonant transformer type supply was shown to be optimal when used in conjunction with a swept frequency. The current and frequency ranges of electrical discharges were continuously variable, and their effect on discharge regeneration performance was studied. The results showed that the discharge frequency had no effect on the regeneration process but did affect spatial distribution. An optimised resonant transformer power supply was designed that was ideally suited for the electrodes used. A novel power modulation strategy, which used a switching frequency phase locked to the ~ iii ~ modulating frequency, was employed which extended the operating range of the discharge to below 10 mA for electrode separations > 7.5 mm. The heat flows within the filter and discharge during regeneration were analysed and the filter damage process was linked to the heat released by the discharge inside the filter wall. Other filter materials were compared based on the findings and Mullite ceramic was identified as a potentially better filter material for Autoselective regeneration. The filtration efficiency is important and was observed to be affected by the Autoselective process. The effect of the discharge on filtration efficiency was studied and the mechanism of particulate re-entrainment was identified as a combination of electrostatic and electro-acoustic forces. The Autoselective technology was successfully implemented in both flow-rig and on-engine tests. Results showed significant reduction in back-pressure for power inputs of ~ 500 W. The understanding of the Autoselective regeneration system has been improved and the research resulted in a novel method of filter regeneration

Supervisory control of complex propulsion subsystems

Modern gasoline and diesel combustion engines are equipped with several subsystems with the goal to reduce fuel consumption and pollutant exhaust emissions. Subsystem synergies could be harnessed using the supervisory control approach. Look-ahead information can be used to potentially optimise power-train control for real time implementation. This thesis delves upon modelling the exhaust emissions from a combustion engine and developing a combined equivalent objective metric to propose a supervisory controller that uses look-ahead information with the objective to reduce fuel consumed and exhaust emissions. In the first part of the thesis, the focus is on diesel engine application control for emissions and fuel consumption reduction.\ua0Model of exhaust emissions in a diesel engine obtained from a combination of nominal engine operation and deviations are evaluated for transient drive cycles.\ua0The look ahead information as a trajectory of vehicle speed and load over time is considered.\ua0The supervisory controller considers a discrete control action set over the first segment of the trip ahead.\ua0The cost to optimise is defined and pre-computed off-line for a discrete set of operating conditions.\ua0A full factorial optimisation carried out off-line is stored on board the vehicle and applied in real-time.\ua0In a first proposal, the subsystem control of the after-treatment system comprising the lean NOx trap and the selective reduction catalyst is considered.\ua0As a next iteration, the combustion engine is added to the control problem.\ua0Simulation comparison of the controllers with the baseline controller offers a 1 % total fuel equivalent cost improvement while offering the flexibility to tailor the controller for different cost objective. In the second part of the thesis, the focus is on cold-start emissions control for modern gasoline engines.\ua0Emissions occurring when the engine is started until the catalyst is sufficiently warm, contribute to a significant proportion of tailpipe pollutant emissions.\ua0Electrically heated catalyst (EHC) in the three way catalyst (TWC) is a promising technology to reduce cold-start emissions where the catalyst can be warmed up prior to engine start and continued after start.\ua0A simulation framework for the engine, TWC with EHC with focus on modeling the thermal and chemical interactions during cold-start was developed.\ua0An evaluation framework with a proposed equivalent emissions approach was developed considering the challenges associated with cold-start emission control.\ua0An equivalent emission optimal post-heating time for the EHC is proposed that adapts to information which is available in a real-time on-line implementation.\ua0The proposed controller falls short of just 1 % equivalent emissions compared to the optimal case

Powertrain Systems for Net-Zero Transport

The transport sector continues to shift towards alternative powertrains, particularly with the UK Government’s announcement to end the sale of petrol and diesel passenger cars by 2030 and increasing support for alternatives. Despite this announcement, the internal combustion continues to play a significant role both in the passenger car market through the use of hybrids and sustainable low carbon fuels, as well as a key role in other sectors such as heavy-duty vehicles and off-highway applications across the globe. Building on the industry-leading IC Engines conference, the 2021 Powertrain Systems for Net-Zero Transport conference (7-8 December 2021, London, UK) focussed on the internal combustion engine’s role in Net-Zero transport as well as covered developments in the wide range of propulsion systems available (electric, fuel cell, sustainable fuels etc) and their associated powertrains. To achieve the net-zero transport across the globe, the life-cycle analysis of future powertrain and energy was also discussed. Powertrain Systems for Net-Zero Transport provided a forum for engine, fuels, e-machine, fuel cell and powertrain experts to look closely at developments in powertrain technology required, to meet the demands of the net-zero future and global competition in all sectors of the road transportation, off-highway and stationary power industries

Renewable diesel fuels and emission control strategies : Implications for occupational exposure, human health, and the environment

Combustion of fossil diesel is a major environmental problem for both the climate and human health. Renewable diesel fuels have been developed and introduced to the market to reduce the net CO2 emissions. Emission control strategies, such as aftertreatment systems, have been implemented to reduce the health hazardous particulate matter (PM) and nitrogen oxides (NOx) emissions. The overall aim of this thesis was to understand the effect of introducing renewable diesel fuels and emission abatement techniques on health relevant exhaust emissions. Laboratory studies were performed to assess the primary and secondary emissions from a heavy-duty diesel engine fueled by the renewable diesel fuels HVO (hydrotreated vegetable oil) and RME (rapeseed methyl ester).The emissions were characterized by detailed particle and gas measurements. We also evaluated the effect of using an aftertreatment system consisting of a diesel oxidation catalyst (DOC) and a diesel particle filter (DPF) on the exhaust emissions. The occupational exposure to diesel exhaust from vehicles in a Swedish modern underground mine was quantified and evaluated in relation to the vehicles’ level of emission reduction technology. The underground ambient concentrations were quantified, and real-world emission factors were calculated. The short-term health effects of HVO exhaust from modern non-road vehicles (2019), with or without the PM fraction, were investigated in a controlled human exposure chamber study. Replacing fossil diesel with HVO and RME significantly reduced the PM emissions, especially the soot emissions(measured as elemental carbon [EC] and equivalent black carbon [eBC]). The fuel change also reduced the hydrocarbon and carbon monoxide emissions, particularly from RME. The significantly reduced hydrocarbon emissions from RME also reduced the secondary aerosol formation, and thus potentially reducing the total atmospheric particle mass burden. Aftertreatment systems containing both a DOC and DPF were very efficient in removing the particle concentrations in the laboratory studies for all fuels. However, as long as a large portion of the vehicle fleet does not have any PM removal systems, the usage of HVO and RME will have a positive impact on overall PM reductions. The average occupational exposure concentration of EC was 7 μg m-3 in the underground mine. This is much lower than the future EU occupational exposure limit (OEL) for diesel exhaust (50 μg EC m-3, from 2026underground). However, epidemiological studies suggest health-based limits closer to 1 μg m-3, which indicates that we should aim to further reduce the exposure. The measured EC exposures ware reduced in areas where vehicles had DPFs. Short-term exposure to HVO exhaust below the EU OELs did not cause severe pulmonary function changes in healthy subjects. However, the subjects experienced an increase in self-rated mild irritation symptoms, and a mild decrease in nasal patency after both the particle-laden and the particle-free HVO exposure. This may indicate irritative effects from exposure to HVO exhaust from modern non-road vehicles below future OELs. Air pollution from combustion sources (not only from vehicles) is a global problem that will be present for years to come. Due to the many adverse effects linked to aerosol air pollution, measures need to be taken to reduce the particle exposures in environmental and occupational settings. The future occupational exposure limit of 50 μg ECm-3 is still much higher than proposed health-based limits. For combustion vehicles, the most efficient way to reduce EC emissions is by using aftertreatment systems focused on removing the PM, such as DPFs. Resources need to be focused on ensuring that such systems are in place and working effectively in all combustion vehicles. This is especially the case in highly exposed areas such as in cities and enclosed work environments

Sizing a conventional diesel oxidation catalyst to be used for RCCI combustion under real driving conditions

[EN] Reactivity controlled compression ignition (RCCI) combustion has demonstrated to be able to avoid the NOx-soot trade-off appearing during conventional diesel combustion (CDC), with similar or better thermal efficiency than CDC under a wide variety of engine platforms. However, a major challenge of this concept comes from the high hydrocarbon (HC) and carbon monoxide (CO) emission levels, which are orders of magnitude greater than CDC, and similar to those of port fuel injected (PFI) gasoline engines. The high HC and CO emissions levels combined with the low exhaust temperatures during RCCI operation could present a challenge for the current exhaust aftertreatment technologies. The objective of this work is to evaluate the potential of a conventional diesel oxidation catalyst (DOC) for light-duty diesel engines when operating under dual-fuel RCCI diesel-gasoline combustion and to define its necessary size to accomplish with the current emissions standards. For this purpose, a 1-D model has been developed and calibrated through gas emissions measurements upstream and downstream the DOC under different engine steady-state conditions. After that, the DOC response in transient conditions has been evaluated by means of vehicle systems simulations under different driving cycles representative of the homologation procedures currently in force around the world. The results show that the HC and CO levels at the DOC outlet are unacceptable considering the different emissions regulations. By this reason, a dedicated study to define the DOC size needed to accomplish the different emissions standards is carried out. The results suggest that, the DOC volume needed to fulfill the type approval regulation limits ranges from four to six times the original volume.The authors gratefully acknowledge General Motors Global Research & Development for providing the engine used in this investigation. The authors also acknowledge FEDER and Spanish Ministerio de Economia y Competitividad for partially supporting this research through TRANCO project (TRA2017-87694-R).García Martínez, A.; Piqueras, P.; Monsalve-Serrano, J.; Lago-Sari, R. (2018). Sizing a conventional diesel oxidation catalyst to be used for RCCI combustion under real driving conditions. Applied Thermal Engineering. 140:62-72. https://doi.org/10.1016/j.applthermaleng.2018.05.043S627214

Powertrain Systems for Net-Zero Transport

The transport sector continues to shift towards alternative powertrains, particularly with the UK Government’s announcement to end the sale of petrol and diesel passenger cars by 2030 and increasing support for alternatives. Despite this announcement, the internal combustion continues to play a significant role both in the passenger car market through the use of hybrids and sustainable low carbon fuels, as well as a key role in other sectors such as heavy-duty vehicles and off-highway applications across the globe. Building on the industry-leading IC Engines conference, the 2021 Powertrain Systems for Net-Zero Transport conference (7-8 December 2021, London, UK) focussed on the internal combustion engine’s role in Net-Zero transport as well as covered developments in the wide range of propulsion systems available (electric, fuel cell, sustainable fuels etc) and their associated powertrains. To achieve the net-zero transport across the globe, the life-cycle analysis of future powertrain and energy was also discussed. Powertrain Systems for Net-Zero Transport provided a forum for engine, fuels, e-machine, fuel cell and powertrain experts to look closely at developments in powertrain technology required, to meet the demands of the net-zero future and global competition in all sectors of the road transportation, off-highway and stationary power industries

Automotive Powertrain Control — A Survey

This paper surveys recent and historical publications on automotive powertrain control. Control-oriented models of gasoline and diesel engines and their aftertreatment systems are reviewed, and challenging control problems for conventional engines, hybrid vehicles and fuel cell powertrains are discussed. Fundamentals are revisited and advancements are highlighted. A comprehensive list of references is provided.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/72023/1/j.1934-6093.2006.tb00275.x.pd