J.M. Herreros

Thermochemical recovery technology for improved modern engine fuel economy – part 1: analysis of a prototype exhaust gas fuel reformer

Exhaust gas fuel reforming has the potential to improve the thermal efficiency of internal combustion engines, as well as simultaneously reduce gaseous and particulate emissions. This thermochemical energy recovery technique aims to reclaim exhaust energy from the high temperature engine exhaust stream to drive catalytic endothermic fuel reforming reactions; these convert hydrocarbon fuel to hydrogen-rich reformate. The reformate is recycled back to the engine as Reformed Exhaust Gas Recirculation (REGR), which provides a source of hydrogen to enhance the engine combustion process and enable high levels of charge dilution; this process is especially promising for modern gasoline direct injection (GDI) engines. This paper presents a full-scale prototype gasoline reformer integrated with a multi-cylinder GDI engine. Performance is assessed in terms of the reformate composition, the temperature distribution across the catalyst, the reforming process (fuel conversion) efficiency and the amount of exhaust heat recovery achieved.

Role of Alternative Fuels on Particulate Matter (PM) Characteristics and Influence of the Diesel Oxidation Catalyst.

The influence of a platinum:palladium (Pt:Pd)-based diesel oxidation catalyst (DOC) on the engine-out particulate matter (PM) emissions morphology and structure from the combustion of alternative fuels (including alcohol-diesel blends and rapeseed oil methyl ester (RME) biodiesel) was studied. PM size distribution was measured using a scanning mobility particulate spectrometer (SMPS), and the PM morphology and microstructure (including size distribution, fractal geometry, and number of primary particles) was obtained using high-resolution transmission electron microscopy (TEM). It is concluded that the DOC does not modify the size or the microstructural parameters of the primary particulates that make up the soot agglomerates. The PM reduction seen in the DOC is due to the trapping effect, and oxidation of the PMs volatile components. The DOC performance in reducing gaseous (e.g., carbon monoxide (CO) and unburnt hydrocarbons (HCs)) and PM emissions at low exhaust temperatures was improved from the combustion of alternative fuels due to the reduced level of engine-out pollutants.

The Use of a Partial Flow Filter to Assist the Diesel Particulate Filter and Reduce Active Regeneration Events

This study investigates the potential of using a partial flow filter (PFF) to assist a wall flow diesel particulate filter (DPF) and reduce the need for active regeneration phases that increase engine fuel consumption. First, the filtration efficiency of the PFF was studied at different engine operating conditions, varying the filter space velocity (SV), through modification of the exhaust gas flow rate, and engine-out particulate matter (PM) concentration. The effects of these parameters were studied for the filtration of different particle size ranges (10-30 nm, 30-200 nm and 200-400 nm). Over the different engine operating conditions, the PFF showed filtration efficiency over 25% in terms of PM number and mass. The PFF filtration behaviour was also investigated at idle engine operation producing a high concentration of nuclei particulates for which the filter was able to maintain 60% filtration efficiency. After a 14 hour soot loading phase, the filter trapping efficiency remained over 20% and showed unexpectedly high small PM filtration efficiency. Finally, a system composed of a PFF placed upstream of a DPF was studied and the filtration efficiency, soot mass accumulated, as well as the pressure increase over a loading period of 7 hours were compared to the ones from a standalone DPF, in order to estimate the beneficial effects of using a PFF to assist the main DPF and reduce the regeneration duration and/or frequency.

Filtered EGR – a step towards an improved NOX/soot trade-off for DPF regeneration

Exhaust gas recirculation (EGR) is currently widely used in commercial diesel engines to provide an effective solution in reducing the levels of nitrogen oxide (NOX) emissions. However, this currently comes at the expense of an exponential increase in particulate matter (PM) emissions resulting directly from the dilution effect (i.e. reduction in oxygen availability), as well as a further penalty arising from the recirculation of the exhaust emissions such as soot and hydrocarbons. In our earlier work it was observed that filtered EGR (FEGR) was able to play a significant role in controlling the soot recirculation penalty and thus improve the overall NOX/soot trade-off. In order to further our understanding of the effect of recirculated exhaust gases and in particular recirculated soot and hydrocarbon (HC), comparisons were made between standard EGR, FEGR and pure nitrogen (N2), a direct cleaner replacement of the exhaust gas. When implementing FEGR, a diesel oxidation catalyst (DOC) and diesel particulate filter (DPF) were introduced into the exhaust to not only filter the soot particulates but reduce the recirculation of HC which can play a role in particulate surface growth. It was observed that the recirculated HC species and soot particles (especially at high load and EGR ratios) play a role in promoting the production and growth of further particles within the combustion chamber. Similarly, by comparing at the same O2 intake concentration as that of FEGR and introducing N2 as the EGR replacement gas, it was possible to correlate the increase in engine-out mass of soot with EGR to the recirculation of soot particles, HC species as well as the presence of H2O and CO2.

Gaseous and Particle Greenhouse Emissions from Road Transport

This chapter discusses the sources and impacts of greenhouse and particle emissions from road transport, as well as future pathways to mitigate their environmental impacts. The main greenhouse gas species considered in greenhouse inventories by the United Nations Framework Convention on Climate Change, such as carbon dioxide, methane and nitrous oxide, are first independently and then conjointly (equivalent carbon dioxide emissions) presented in the different sections of this chapter. Tailpipe greenhouse emissions produced by the propulsion and/or after-treatment systems (direct tank-to-wheel) and those emitted during the life cycle of fuels and vehicles (indirect well-to-tank) are both accounted for. Particle emissions are also addressed from a broad environmental standpoint. Improvements in vehicle fuel economy, behavioural changes in society in order to avoid unnecessary journeys and a higher market penetration rate of low-carbon vehicle technologies and energy carriers are the pathways required to achieve an overall reduction in greenhouse gas emissions and the weather-related disasters associated with them.

Road Vehicle Technologies and Fuels

Road vehicles are an indispensable part of human daily lives. Compression and spark ignition powertrains have been continuously evolving towards more efficient and cleaner technologies. The social awareness of the impact on the environment and human health of the toxic pollutants emitted during the combustion of fossil fuels has led to the introduction of legislation that restricts the emission limits of road vehicles. Vehicle manufacturers are researching and rapidly developing technologies that can offer both reduced fuel consumption and low emission of nitrogen oxides (NOx), particulate matter (PM), carbon dioxide, carbon monoxide and unburnt hydrocarbons. This chapter provides an overview of the basic road vehicle transportation concepts from the past to the future trends, from the development of the precise fuel injection systems to recent research in new near-zero NOx-PM emission combustion modes. Apart from the engine itself, alternative fuels can have benefits in pollution depletion. Bioalcohols, liquefied petroleum gas, compressed natural gas or hydrogen for spark ignition engines and fatty acid methyl esters or hydrotreated vegetable oil for diesel engines are under research. The benefits and barriers of these alternative fuels have been discussed. The inherent trade-off between pollutants and high-efficiency engines and the use of after-treatment systems to reduce engine-out emissions are also explored. The current state of the market share as well as a forecast for the near future are also parts of this chapter.

Influence of Three-Way Catalyst on Gaseous and Particulate Matter Emissions During Gasoline Direct Injection Engine Cold-start

The development of gasoline direct injection (GDI) engines has provided a strong alternative to port fuel injection engines as they offer increased power output and better fuel economy and carbon dioxide emissions. However, particulate matter (PM) emission reduction from GDI still remains a challenge that needs to be addressed in order to fulfil the increasingly stricter environmental regulations. A large number of the total particulate emissions during driving cycles are produced during the engine cold-start. Therefore, controlling PM during cold-start events will significantly reduce the final PM output. This research work provides an understanding of PM characterisation from a 2 l four-cylinder GDI engine during cold-start. Gaseous emissions including hydrocarbon (HC) speciation studies are also carried out preand posta Euro 6 compliant three-way catalyst (TWC). In addition, particulate size distribution and total particulate number were recorded for the first 280 seconds after the engine cold-start. Large concentrations of carbon monoxide, propane, acetaldehyde, formaldehyde, ethanol, toluene and ethylene were emitted during the first 70–90 seconds from the engine start. Gaseous emissions were reduced on the catalyst at temperatures higher than 290°C, with the catalyst reaching almost 100% removal efficiency at 350°C. The effect of the TWC on PM emissions has been analysed for the different PM diameter ranges. A reduction of particles smaller than 20 nm was observed as well as a reduction in the accumulation mode. In order to understand the nature of the particles emitted during cold-start, transmission electron microscope (TEM) grids were used for particulate collection at the engine start and after 80 seconds and 140 seconds of engine operation. A peak of 1.4 × 108 particles was produced at the engine start and this steadily reduced to 3 × 107 in 50 seconds. The TEM micrographs showed solid particles with similar fractal-like shapes.