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Coventry, United Kingdom

Daniel R.,University of Birmingham | Xu H.,University of Birmingham | Xu H.,Tsinghua University | Wang C.,University of Birmingham | And 2 more authors.
Applied Energy | Year: 2013

To meet the needs of fuel security and combat the growing concerns of CO2 emissions, the automotive industry is seeking solutions through biofuels. Traditionally, when supplying biofuel blends to the combustion chamber, the blend is mixed externally prior to its injection in one location. This location occurs either before the cylinder (port-fuel injection, PFI), or directly into the cylinder (direct-injection, DI). However, the use of dual-injection allows the in-cylinder blending of two fuels at any blend ratio, when combining the two locations (PFI and DI). This injection strategy offers increased flexibility as the blend ratio can be changed instantaneously according to engine speed and load demand and fuel availability. Previous work by the authors has reported the improved combustion performance of dual-injection with 25% blends (in gasoline) of a new biofuel candidate: 2,5-dimethylfuran (DMF). This current investigation extends the analysis to include the gaseous emissions of various DMF blends (25%, 50% and 75%) from 3.5bar to 8.5bar IMEP and the particulate matter (PM) emissions of similar fraction ethanol blends at a selected condition of 5.5bar IMEP. Compared to DI, dual-injection offers reduced CO and CO2 emissions and comparable HC emissions. The mean PM diameter is decreased and the accumulation mode particles are negligible compared to DI. However, the implication of the higher combustion pressures is an increase in NOx due to reduced charge-cooling. © 2012 Elsevier Ltd.

Aleiferis P.G.,University College London | Serras-Pereira J.,University College London | Richardson D.,Jaguar Advanced Powertrain Engineering
Fuel | Year: 2013

Research into novel internal combustion engines requires consideration of the diversity in future fuels that may contain significant quantities of bio-components in an attempt to reduce CO2 emissions from vehicles and contribute to energy sustainability. However, most biofuels have different chemical and physical properties to those of typical hydrocarbons; these can lead to different mechanisms of mixture preparation and combustion. The current paper presents results from an optical study of combustion in a direct-injection spark-ignition research engine with gasoline, iso-octane, ethanol and butanol fuels injected from a centrally located multi-hole injector. Methane was also employed by injecting it into the inlet plenum of the engine to provide a benchmark case for well-mixed 'homogeneous' charge preparation. Crank-angle resolved flame chemiluminescence images were acquired and post-processed for a series of consecutive cycles for each fuel, in order to calculate in-cylinder rates of flame growth and motion. In-cylinder pressure traces were used for heat release analysis and for comparison with the image-processing results. All tests were performed at 1500 RPM with 0.5 bar intake plenum pressure. Stoichiometric (φ = 1.0) and lean (φ = 0.83) conditions were considered. The combustion characteristics were analysed with respect to laminar and turbulent burning velocities obtained from combustion bombs in the literature and from traditional combustion diagrams in order to bring all data into the context of current theories and allow insights by making comparisons were appropriate. © 2013 Elsevier Ltd. All rights reserved.

Serras-Pereira J.,University College London | Aleiferis P.G.,University College London | Richardson D.,Jaguar Advanced Powertrain Engineering
Combustion Science and Technology | Year: 2013

Future automotive fuels are expected to contain significant quantities of bio-components. This poses a great challenge to the designers of novel low-CO2 internal combustion engines because biofuels have very different properties to those of most typical hydrocarbons. The current article presents results of firing a direct-injection spark-ignition optical research engine on ethanol and butanol and comparing those to data obtained with gasoline and iso-octane. A multihole injector, located centrally in the combustion chamber, was used with all fuels. Methane was also employed by injecting it into the inlet plenum to provide a benchmark case for well-mixed "homogeneous" charge preparation. The study covered stoichiometric and lean mixtures (λ = 1.0 and λ = 1.2), various spark advances (30-50° CA), a range of engine temperatures (20-90°C), and diverse injection strategies (single and "split" triple). In-cylinder gas sampling at the spark-plug location and at a location on the pent-roof wall was also carried out using a fast flame ionization detector to measure the equivalence ratio of the in-cylinder charge and identify the degree of stratification. Combustion imaging was performed through a full-bore optical piston to study the effect of injection strategy on late burning associated with fuel spray wall impingement. Combustion with single injection was fastest for ethanol throughout 20-90°C, but butanol and methane were just as fast at 90°C; iso-octane was the slowest and gasoline was between iso-octane and the alcohols. At 20°C, λ at the spark plug location was 0.96-1.09, with gasoline exhibiting the largest and iso-octane the lowest value. Ethanol showed the lowest degree of stratification and butanol the largest. At 90°C, stratification was lower for most fuels, with butanol showing the largest effect. The work output with triple injection was marginally higher for the alcohols and lower for iso-octane and gasoline (than with single injection), but combustion stability was worse for all fuels. Triple injection produced a lower degree of stratification, with leaner λ at the spark plug than single injection. Combustion imaging showed much less luminous late burning with tripe injection. In terms of combustion stability, the alcohols were more robust to changes in fueling (λ = 1.2) than the liquid hydrocarbons. © 2013 Copyright J. Serras-Pereira, P. G. Aleiferis, and D. Richardson.

Serras-Pereira J.,University College London | Aleiferis P.G.,University College London | Richardson D.,Jaguar Advanced Powertrain Engineering
Fuel | Year: 2012

The latest generation of fuel systems for direct-injection spark-ignition engines uses injection nozzles that accommodate a number of holes with various angles in order to offer flexibility in in-cylinder fuel targeting over a range of engine operating conditions. However, the high-injection pressures that are needed for efficient fuel atomisation can lead to deteriorating effects with regards to engine exhaust emissions (e.g. unburned hydrocarbons and particulates) from liquid fuel impingement onto the piston and liner walls. Eliminating such deteriorating effects requires fundamental understanding of in-cylinder spray development processes, taking also into account the diversity of future commercial fuels that can contain significant quantities of bio-components with very different chemical and physical properties to those of typical liquid hydrocarbons. This paper presents high-speed imaging results of spray impingement onto the liner of a direct-injection spark-ignition engine, as well as crank-angle resolved wall heat flux measurements at the observed locations of fuel impingement for detailed characterisation of levels and timing of impingement. The tests were performed in a running engine at 1500 RPM primarily at low load (0.5 bar intake pressure) using 20, 50 and 90 °C engine temperatures. Gasoline, iso-Octane, Butanol, Ethanol and a blend of 10% Ethanol with 90% Gasoline (E10) were used to encompass a range of current and future fuel components for spark-ignition engines. The collected data were analysed to extract mean and standard deviation statistics of spray images and heat flux signals. The results were also interpreted with reference to physical properties and evaporation rates predicted by a single droplet model for all fuels tested. © 2011 Elsevier Ltd. All rights reserved.

Serras-Pereira J.,University College London | Aleiferis P.G.,University College London | Richardson D.,Jaguar Advanced Powertrain Engineering
International Journal of Engine Research | Year: 2015

This article presents results from a comprehensive optical study of a direct-injection spark-ignition research engine running on gasoline, iso-octane, ethanol, n-butanol and E10 fuels injected from a multi-hole central vertically positioned injector. The analysis was based on images of spray development, spark discharge and combustion to understand the effects of early and late injection strategies on in-cylinder phenomena. Specifically, 'single'-injection strategies from early to late intake stroke as well as multiple 'split' injection events with triple pulses in the early intake stroke or double pulses in the intake stroke and late compression stroke were investigated. The engine was run at 1500 r/min at part- and full-load conditions (0.5 and 1.0 bar inlet plenum pressure, respectively). Engine coolant temperatures of 20°C-90°C were employed to understand how fuel volatility was related to the phenomena observed. The sprays were imaged over a series of cycles primarily by laser sheet illumination on one vertical and two horizontal planes to identify three-dimensional aspects of the spray's development and its interactions with the incoming flow, valves, piston and liner. There was a clear fuel-impingement trade-off between early and late injection timings. The spark discharge was also imaged with all injection strategies and clear differences were observed. Selective combustion imaging provided insights into the flame's growth and motion with early and double early-late split injection strategies. The double earlylate injection strategy demonstrated the potential for control of the mixture formation and flow field over the early flame development stage of combustion. © Institution of Mechanical Engineers.

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