Effect of hydrogen-diesel fuel co-combustion on exhaust emissions with verification using an in–cylinder gas sampling technique

AbstractThe 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. The tests were performed at fixed diesel injection periods, with hydrogen added to vary the engine load between 0 and 6 bar IMEP. In addition, a novel in–cylinder gas sampling technique was employed to measure species concentrations in the engine cylinder at two in–cylinder locations and at various instants during the combustion process.The results showed a decrease in the particulates, CO and THC emissions and a slight increase in CO2 emissions with the addition of hydrogen, with fixed diesel fuel injection periods. NOx emissions increased steeply with hydrogen addition but only when the combined diesel and hydrogen co-combustion temperatures exceeded the threshold temperature for NOx formation. The in–cylinder gas sampling results showed higher NOx levels between adjacent spray cones, in comparison to sampling within an individual spray cone

The influence of straight vegetable oil fatty acid composition on compression ignition combustion and emissions

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 Chlorella protothecoides were tested, with all of the fuels heated to 60°C, at constant injection timing and constant ignition timing at a constant engine speed of 1200 rpm. All of the vegetable oils exhibited a duration of ignition delay within ±0.6 CAD of that displayed by a reference fossil diesel, but displayed much reduced rates of peak heat release rate. The duration of ignition delay was found to increase with an increasing carbon to hydrogen ratio of the vegetable oils, implicating the fatty acid alkyl chain as the primary driver of low temperature reactivity. Peak heat release rates decreased with decreasing vegetable oil viscosity, suggesting a significant degree of fuel cylinder wall and piston bowl impingement. At both injection timings, emissions of NOx were lower for all of the vegetable oils relative to the reference fossil diesel, while those of CO, THC and particulate matter were higher and sensitive to the injection timing

Opening the black box: soil microcosm experiments reveal soot black carbon short-term oxidation and influence on soil organic carbon mineralisation

Soils hold three quarters of the total organic carbon (OC) stock in terrestrial ecosystems and yet we fundamentally lack detailed mechanistic understanding of the turnover of major soil OC pools. Black carbon (BC), the product of the incomplete combustion of fossil fuels and biomass, is ubiquitous in soils globally. Although BC is a major soil carbon pool, its effects on the global carbon cycle have not yet been resolved. Soil BC represents a large stable carbon pool turning over on geological timescales, but research suggests it can alter soil biogeochemical cycling including that of soil OC. Here, we established two soil microcosm experiments: experiment one added 13C OC to soil with and without added BC (soot or biochar) to investigate whether it suppresses OC mineralisation; experiment two added 13C BC (soot) to soil to establish whether it is mineralised in soil over a short timescale. Gases were sampled over six-months and analysed using isotope ratio mass spectrometry. In experiment one we found that the efflux of 13C OC from soil decreased over time, but the addition of soot to soil significantly reduced the mineralisation of OC from 32% of the total supplied without soot to 14% of the total supplied with soot. In contrast, there was not a significant difference after the addition of biochar in the flux of 13C from the OC added to the soil. In experiment two, we found that the efflux 13C from soil with added 13C soot significantly differed from the control, but this efflux declined over time. There was a cumulative loss of 0.17% 13C from soot over the experiment. These experimental results represent a step-change in understanding the influence of BC continuum on carbon dynamics, which has major consequences for the way we monitor and manage soils for carbon sequestration in future

Algal biomass and diesel emulsions: An alternative approach for utilizing the energy content of microalgal biomass in diesel engines

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 an alternative method of utilizing the energy content of microalgae through the preparation of wet algal biomass slurry/fossil diesel emulsions containing up to 6.6% wt/wt algae biomass, using a specific surfactant combination, for direct injection diesel engine combustion of microalgae without prior biomass drying or lipid extraction. A high lipid containing green microalgae, Chlorella sorokiniana, was used to produce algal biomass for the study. The preparation of wet algal slurry/diesel emulsions from algae grown under standard conditions, and also those under conditions intended to increase cellular lipid content or growth rates was investigated, and in all cases a surfactant pack of Span80, CTAB and butanol was found to produce a stable emulsion. A correlation between the engine work produced during combustion of the emulsions in a modern direct injection compression ignition and the lower heating value of the wet slurry emulsions was found, with no evidence of individual algae cells persisting to the engine exhaust. Engine exhaust emissions of nitrogen oxides (NOx) and particulate matter were lower for all of the wet algal slurry/diesel emulsions relative to a reference fossil diesel tested under similar conditions, while in the case of the emulsion prepared from algal biomass to which a flocculating agent had been added, emissions of carbon monoxide (CO) were found to increase significantly

Influence of Combustion Characteristics and Fuel Composition on Exhaust PAHs in a Compression Ignition Engine

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 PAHs produced from combustion of fossil diesel fuel and several model fuel blends of n-heptane, toluene and methyl decanoate in a single-cylinder diesel research engine based on a commercial light duty automotive engine. It was found that the level of total PAHs emitted by the various fuel blends decreased with increasing fuel ignition delay and premixed burn fraction, however, where the ignition delay of a fuel blend was decreased with use of an ignition improving additive the level of particulate phase PAH also decreased. Increasing the level of toluene present in the fuel blends decreased levels of low toxicity of two to four ring PAH, while displacing n-heptane with methyl decanoate increased particulate phase adsorbed PAH. Overall, the composition of the fuels investigated was found to have more influence on the concentration of exhaust PAHs formed than that of combustion characteristics, including ignition delay, peak heat release rate and the extent of the premixed burn fractions