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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.

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This paper presents an experimental investigation on the influence of engine speed on the combustion characteristics of a Gardener compression ignition engine fueled with rapeseed methyl esther (RME). The engine has a maximum power of 14.4 kW and maximum speed of 1500 rpm. The experiment was carried out at speeds of 750 and 1250 rpm under loads of 4, 8, 12, 16 and 18 kg. Variations of cylinder pressure with crank angle degrees and cylinder volume have been examined. It was found that RME demonstrated short ignition delay primarily due to its high cetane number and leaner fuel properties (equivalence ratio (φ) = 0.22 at 4kg). An increase in thermal efficiency but decrease in volumetric efficiency was recorded due to increased brake loads. Variations in fuel mass flow rate, air mass flow rate, exhaust gas temperatures and equivalence ratio with respect to brake mean effective pressure at engine speeds of 750 and 1250 rpm were also demonstrated in this paper. Higher engine speed of 1250 rpm resulted in higher fuel and air mass flow rates, exhaust temperature, brake power and equivalent ratio but lower volumetric efficiency. Keywords— combustion characteristics, engine performance, engine speed, rapeseed methyl Esther

Highlights Increasing unsaturation increased soot size, mass, and number concentrations. Increasing unsaturation increased particle phase PAHs and soot particle carcinogenicity. Soot carcinogenicity decreased with the soot particle number. Soot carcinogenicity decreased with soot particle mass and size. Temperature increase from 1050 to 1350 °C decreased soot carcinogenicity.

This paper examines the effect of equalizing ignition delay in a compression ignition engine. Two sets of tests were conducted. A constant injection timing tests with start of fuel injection at 10 o CAD BTDC and a constant ignition timing tests while also keeping the 10 o CAD BTDC injection and adding ignition improver (2ethylhexylnitrate -2EHN) to the fuel mixtures. Soot particles were characterised using DMS-500 instrument in terms of mass, size, and number. The experimental results showed that adding 2-EHN to the model fuel blends reduced the soot surface area, soot mass concentration and soot mean size. Replacing 20% (vol) of a C7-heptane, with 20% of methyl-decanoate (an oxygenated C11 molecule) did not affect the ignition delay or rates of fuel air premixing, the peak in-cylinder pressure and heat release rates. Toluene addition (0 -22.5% by vol) to heptane increased the mean size of the soot particles generated by only 3% while also resulting in a slight increase in the peak cylinder pressure and peak heat release rates. Blending toluene and methyl-decanoate into heptane without adding-2EHN increased the premix phase fraction by at least 13%. However, adding 2EHN (400 -1500ppm), the premixed phase fraction decreased by at least 11%.

Petrov-Galerkin finite element scheme for systematic analysis of the dynamics of a rising Taylor bubble and general free surface flow problems is derived and implemented. The validity of the scheme is confirmed by simulating the buoyancy-driven motion of a Taylor bubble through a stagnant Newtonian liquid in a vertical pipe characterised by dimensionless inverse viscosity number and Eötvös number of magnitude 111 and 189, respectively. Comparison of the numerical results for the steady state features defining the nose, film, and bottom regions around the bubble with the experiment shows a good agreement between the numerical simulation and the experiment. The percentage deviation of the numerical computed rise velocity, equilibrium film thickness, and stabilisation length ahead of the bubble from the experimental determined values are 8.4%, 2.3%, and 9.5%, respectively.