Paul Hellier

• PhD, MEng
• Professor of Sustainable Energy Engineering at University College London

Polycyclic aromatic hydrocarbons (PAHs) are potentially carcinogenic pollutants emitted by diesel engines, both in the gas phase and adsorbed onto the surface of particulate matter (PM). There remains limited understanding of the complex and dynamic competing mechanisms of PAH formation, growth and oxidation in the gas phase, and their adsorption o...

Spent coffee grounds (SCG) are a potentially valuable source of lipids for sustainable production of biofuels. However, there are several feedstock properties and solvent extraction parameters that can impact on the oil yield and quality, potentially reducing the possible environmental benefits of deriving oils from this waste stream. This study pr...

This paper reports an experimental investigation into the effects of fuel composition on the exhaust emission of toxic polycyclic aromatic hydrocarbons (PAHs) from a diesel engine, operated at both constant fuel injection and constant fuel ignition modes. The paper quantifies the US EPA (United State Environmental Protection Agency) 16 priority PAH...

Recently, the production of sustainable biofuels from algal biomass has gained significant attention and been investigated as a potential replacement of fossil fuel. However, existing downstream processes for producing biodiesel from algae cells are complex, highly energy-intensive, and have high economic and environmental cost. Therefore, this wor...

Lipids extracted from spent coffee grounds (SCG) are a potentially promising feedstock for biodiesel production if the relatively high free fatty acid (FFA) portion of the oil can be successfully converted into methyl esters, and the resulting biodiesel found to have acceptable combustion and emissions performance. This study presents experimental...

div class="section abstract"> The development of new fuels for internal combustion engines (ICE) requires further technical support by understanding the pollutant formation mechanism in various phases of combustion so that emissions can be minimised. This research will therefore utilize a bespoke in-cylinder sampling system to analyse the precursor...

Expanding the use of sustainable fuels in hard to decarbonise transport vehicles utilising heavy-duty engines is urgently required to reduce greenhouse gas emissions from sectors reliant on these engines. As...

Rapidly decreasing urban air quality and the resultant health impacts are of increasing global concern, with an estimated 7 million premature deaths worldwide attributable to airborne pollutants. Many European and North American cities are increasingly implementing emissions monitoring and control schemes, however, those in the Middle East, Africa,...

Renewable alternatives to fossil diesel (FD) including fatty acid methyl ester (FAME) biodiesel have become more prevalent. However, toxicity of exhaust material from their combustion, relative to the fuels they are displacing has not been fully characterised. This study was carried out to examine particle toxicity within the lung epithelium and th...

Air pollution in many major cities is endangering public health and is causing deterioration of the environment. Particulate emissions (PM) contribute to air pollution as they carry toxic polyaromatic hydrocarbons (PAHs) on their surface. Abatement of PM requires continuous strict emission regulation and, in parallel, the development of fuels with...

Air pollution has reached critical levels in many major industrial cities, endangering public health, deteriorating the environment, and causing harm to property and landscape. The particulate emissions (PM) from propulsion which contribute to air pollution vary greatly in size and composition, conveying carcinogenic polyaromatic hydrocarbons (PAHs...

This paper examines the effect of equalizing ignition delay in a compression ignition engine. Two sets of tests were conducted, i.e. a set of constant injection timing tests with start of fuel injection at 10° crank angle degree (CAD) before top dead center (BTDC) and a set of constant ignition timing tests while also keeping the 10° CAD BTDC injec...

This paper examines the effect of equalizing ignition delay in a compression ignition engine. Two sets of tests were conducted, i.e. a set of constant injection timing tests with start of fuel injection at 10° crank angle degree (CAD) before top dead center (BTDC) and a set of constant ignition timing tests while also keeping the 10° CAD BTDC injec...

Screening of a variety of bioderived furanic molecules was performed in order to improve our understanding of how this class of molecules respond during compression-ignition combustion, after blending with diesel fuel. Reducing carbon emissions is possible through the use of “2nd generation” carbon neutral biofuels, the sources of which are from no...

The ability of ammonia to act as a hydrogen carrier, without the drawbacks of hydrogen gas-storage costs and low stability-renders it a potential solution to the decarbonisation of transport. This study combines both modelling and experimental techniques to determine the effect of varying the degree of aspiration of ammonium hydroxide (NH4OH) solut...

Biofuels may reduce road transport carbon intensity; however, it is uncertain whether displacing fossil diesel would alter the engine-derived particulate toxicity. The primary objective of this work was to determine whether there is a fuel effect on the comparative in vitro toxicity of biodiesel exhaust particulates relative to those from fossil di...

Particulate matter (PM) is emitted from a range of combustion sources, can vary greatly in properties, and is able to penetrate deep into the human lungs, conveying carcinogenic PAHs present on the particle surface. Alcohol based biofuels have been shown to potentially reduce PM emissions when displacing fossil fuels. To improve understanding of th...

An investigation into the exhaust emissions of carcinogenic polycyclic aromatic hydrocarbons (PAHs) from a diesel engine was reported. The study is reinforced by the experimental results obtained from a tube reactor aimed at examining the PAH formation processes from these fuels. The paper cantered on the 16 priority PAHs suggested by the United St...

This paper concerns the effect of unsaturation of hydrocarbons (single, double, and triple bonds) on soot particle characteristics (mass, number, and size) and on the carcinogenicity of soot particles. The soot particles were produced from oxygen-free pyrolysis of five hydrocarbons, namely: propane, propylene, ethane, ethylene, and acetylene. The c...

A significant amount of harmful emissions pass unreacted through catalytic after-treatment devices for IC engines before the light-off temperature is reached, despite the high conversion efficiency of these systems in fully warm conditions. Further tightening of fleet targets and worldwide emission regulations will make a faster catalyst light-off...

Functionalized graphene sheets (FGS) have proven to be an effective nanoparticle additive for jet fuels. In this study, the reactive force field (ReaxFF) molecular dynamics (MD) simulation is employed to investigate the initiation mechanisms of JP-10 pyrolysis and oxidation with FGS in comparison with normal JP-10 reactions. ReaxFF-nudged elastic b...

Better understanding of combustion and formation of exhaust gas pollutants of fuels is needed in order to meet stringent regulation standards of a diesel engine. The cetane number is one of the most-cited indicators of diesel fuel quality. This paper presents experimental studies with a wide range of fuels to investigate the effect of cetane number...

Aluminium hydride (AlH3) has a great potential for a variety of propulsion and energy storage applications. In this study, the ReaxFF reactive force field molecular dynamics simulation is employed to investigate the fundamental reaction mechanisms of thermal decomposition and oxidation of AlH3. The effects of an oxide layer and/or defect are examin...

Current biofuels for diesel engines are largely derived from food crops and there is significant concern, recognised by legislation, that such fuels do not result in net reductions of greenhouse gas emissions when considering the entirety of the production to usage lifecycle. A potential alternative approach is to utilise the lipid content of organ...

Spent coffee grounds (SCG) are the main residues of the coffee beverage industry, and a potentially valuable source of energy-dense lipids. The present study investigates the effect of temperature, pressure and duration on the pressurized solvent extraction of lipids from dried SCG to evaluate their impact on oil extraction efficiency, composition...

Concerns as to the adverse effects of diesel engine exhaust on urban air quality have resulted in increasingly stringent emissions legislation, with the prospect of many major global cities potentially banning diesel vehicles. Emissions of nitrogen oxides (NOx) and particulate matter (PM) are linked to increases in premature mortality, and the simu...

Spent coffee grounds (SCG) are a potentially sustainable source of C16-C18 triglycerides. This study investigates known solvent extraction technologies with a wide range of solvents for lipid extraction from SCGs, and determines the effect of solvent selection and process temperature on the extraction efficiency and composition of the obtained oil....

The influence of carbon number of seven hydrocarbons (methane, ethane, propane, n-butane, i-butane, heptane and toluene) on PAH formation was investigated in a laminar tube reactor. The hydrocarbons underwent oxygen-free pyrolysis within the temperature range of 1050-1350 °C at a fixed carbon concentration of 10,000 ppm on C 1 basis. Particulate an...

Ethanol is a potential alternative to conventional fossil fuels. However, the required dewatering process to produce anhydrous ethanol is extremely energy-intensive and expensive. A promising solution is the direct use of hydrous ethanol for combustion applications, which can dramatically reduce the production cost. Many researchers have undertaken...

Spent coffee grounds (SCGs) and roasted defective coffee beans (RDCBs), are a potentially sustainable source for biofuel production if the processing of these residues, and the recovery of energy-dense lipids, can be undertaken in an energy efficient way. A necessary step in solvent extraction of lipids is prior drying of the feedstock, and this ca...

The co-combustion of diesel fuel with H2 presents a promising route to reduce the adverse effects of diesel engine exhaust pollutants on the environment and human health. This paper presents the results of H2-diesel co-combustion experiments carried out on two different research facilities, a light duty and a heavy duty diesel engine. For both engi...

Lignocellulosic materials have been identified as potential carbon–neutral sources of sustainable power production. Catalytic conversion of lignocellulosic biomass results in liquid fuels with a variety of aromatic molecules. This paper investigates the combustion characteristics and exhaust emissions of a series of alkylbenzenes, of varying number...

Sustainable future fuels are likely to be produced by a wide range of processes, and there exists the opportunity to engineer these fuels so that they burn more efficiently and produce fewer harmful emissions. Such potential is especially important within the context of reducing the emissions of both greenhouse gases (GHG) and toxic pollutants that...

The conversion of lignocellulosic biomass to liquid fuels presents an alternative to the current production of renewable fuels for IC engines from food crops. However, realising the potential for reductions in net CO2 emissions through the utilisation of, for example, waste biomass for sustainable fuel production requires that energy and resource i...

Engineering systems such as gas turbines and internal combustion engines utilise gaseous fuels which produce toxic substances when they are burnt. Among these substances are solid soot particles and gas phase polycyclic aromatic hydrocarbons (PAHs). The link between soot and PAHs has long been established. Firstly, PAHs assemble themselves into lar...

Future fuels for compression ignition engines will be required both to reduce the anthropogenic carbon dioxide emissions from fossil sources and to contribute to the reductions in the exhaust levels of pollutants, such as nitrogen oxides and particulate matter. Via various processes of biological, chemical and physical conversion, feedstocks such a...

This paper presents a study undertaken on a naturally aspirated, direct injection diesel engine investigating the combustion and emission characteristics of CH4-CO2 and CH4-CO2-H2 mixtures. These aspirated gas mixtures were pilot-ignited by diesel fuel, while the engine load was varied between 0 and 7 bar IMEP by only adjusting the flow rate of the...

This paper presents a H2-diesel fuel co-combustion study undertaken on a supercharged, direct injection, diesel engine investigating the combustion characteristics and emissions production at a range of engine loads (IMEP), EGR levels and intake air boosting conditions. The utilisation of EGR and intake air boost with H2-diesel fuel co-combustion a...

This paper presents the results of an experimental study that was carried out to determine the conversion rates to particulate matter (PM) of several liquid fuel hydrocarbon molecules and specific carbon atoms within those molecules. The fuels investigated (ethanol, n-propanol, i-propanol, acetone, and toluene) were blended in binary mixtures with...

This paper presents the results of an experimental study that was carried out to determine the conversion rates to particulate matter (PM) of several liquid fuel hydrocarbon molecules and specific carbon atoms within those molecules. The fuels investigated (ethanol, n-propanol, i-propanol, acetone, and toluene) were blended in binary mixtures with...

The use of algal biomass for the production of sustainable biofuels has attracted significant interest due to the fast reproduction rates and high lipid content of many microalgal species. However, existing methods of extracting algal cellular lipids are complex and expensive, with regards to both energy input and economic costs. This work explores...

Development of new fuels and engine combustion strategies for future ultra-low emission engines requires a greater level of insight into the process of emissions formation than is afforded by the approach of engine exhaust measurement. The paper describes the development of an in-cylinder gas sampling system consisting of a fast-acting, percussion-...

The autoignition timing of 1-Hexene was controlled in a Homogeneous Charge Compression Ignition (HCCI) engine by reacting the fuel with ozone-containing air prior to its combustion. The experiments were conducted in a single cylinder research engine instrumented with an cylinder pressure sensor. The fuel was chemically characterised using Nuclear M...

Renewable alternatives to fossil fuels are necessary for the reduction of anthropogenic greenhouse gas emissions, the increased atmospheric concentrations of which are resulting in global climate change. Biodiesel, fatty acid esters prepared from the reaction of triglycerides with alcohols, is a potentially sustainable fuel for compression ignition...

The metabolic engineering of photosynthetic microbes for production of novel hydrocarbons presents an opportunity for development of advanced designer biofuels. These can be significantly more sustainable, throughout the production-to-consumption lifecycle, than the fossil fuels and crop-based biofuels they might replace. Current biofuels, such as...

The paper is concerned with particulate formation from the fuels oleic acid and methyl oleate. In particular the paper reports, quantitatively, the propensity of individual carbon atoms in these two molecules in being converted to particulate. The conversion of individual carbon atoms to particulate was traced by ‘labelling’ individual carbon atoms...

This paper presents experimental studies carried out on a modern direct injection compression ignition engine supplied with a range of straight vegetable oils to investigate the effect of oil fatty acid composition on combustion and emissions. Seven oils, those of corn, groundnut, palm, rapeseed, soybean, sunflower and the micro-algae species Chlor...

Copyright © 2014 SAE International.Improvements in the efficiency of internal combustion engines and the development of renewable liquid fuels have both been deployed to reduce exhaust emissions of CO 2 . An additional approach is to scrub CO 2 from the combustion gases, and one potential means by which this might be achieved is the reaction of com...

The paper presents an experimental investigation of hydrogen-diesel fuel co-combustion carried out on a naturally aspirated, direct injection diesel engine. The engine was supplied with a range of hydrogen-diesel fuel mixture proportions to study the effect of hydrogen addition (aspirated with the intake air) on combustion and exhaust emissions. Th...

Substitution of conventional feedstock with waste based alternatives is one route towards both remediation and reducing costs associated with production of algal biomass. This work explores whether exhaust gases and wastewater can replace conventional feedstock in the production of biomass from Chlorella sorokiniana. Exhaust gases were used to augm...

Successfully designing and making effective of use of the next generation of liquid fuels, which will be derived from a range of biomass and fossil sources, requires an understanding of the interactions between structurally similar and dissimilar fuel components when utilised in current engine technology. Interactions between fuel components can in...

In developing future fuels there is an opportunity to make use of advances in many fields of science and engineering to ensure that such fuels are sustainable in both production and utilization. One such advance is the use of synthetic biology to re-engineer photosynthetic micro-organisms such that they are able to produce novel hydrocarbons direct...

A primary motivation for the development of future fuels is to halt the increasing concentration of atmospheric carbon dioxide. As such, a fuel that can potentially be produced from a feedstock of alcohols and atmospheric carbon dioxide is an attractive proposition. Symmetrical carbonate esters may thus offer a sustainable means of converting alcoh...

Future fuels will be developed from a variety of biomass and fossil sources, and must seek to address the adverse environmental impacts of current fossil fuel usage. To this end, understanding how the molecular structure of a fuel impacts on the processes of combustion and emissions production is critical in selecting suitable feed-stocks and conve...

Future fuels will be developed from a variety of biomass and fossil sources, and this presents an opportunity to design new fuels that carry a much reduced environmental burden. To this end, understanding how the molecular structure of a fuel impacts on the processes of combustion and emissions production is critical in selecting suitable feed-stoc...

At present, biodiesel is primarily comprised of fatty acid methyl esters (FAMEs) obtained by the transesterification of a variety of vegetable oils with methanol. However, transesterification can be carried out with a wide variety of alcohols other than methanol. This paper presents experimental studies carried out on a diesel engine supplied with...

Diesel fuels usually comprise a wide range of compounds having different molecular structures which can affect both the fuel's physical properties and combustion characteristics. In future, as synthetic fuels from fossil and sustainable sources become increasingly available, it could be possible to control the fuel's molecular structure to achieve...

The present paper describes a method of controlling the time of ignition in homogeneous-charge compression ignition (HCCI) combustion. In the described experiments some control of ignition timing in HCCI combustion is achieved through alteration of the fuel molecular structure using a chemical reaction of the fuel with ozone, prior to introduction...