Biodiesel, the fatty acid alkyl esters derived from vegetable oils, animal fats, or waste cooking oils, is an alternative to diesel fuel. One of the major technical issues with the use of biodiesel is its susceptibility to oxidation. Oxidation of biodiesel is a complex process which involves a number of mechanisms producing an array of chemical components such as aldehydes, acids, ketones, and oligomeric compounds. These components in turn increase the viscosity and deposits in the fuel beyond acceptable levels. A variety of factors affect the level of these decomposition products as well as the rate of formation and decay. These factors include the temperature, presence of light, catalytic metals in the fuel system, sump oil, or storage containers, type of biodiesel, fatty acid profile, blend level, other contaminants, and presence of antioxidants. This paper examines the relevant factors influencing the biodiesel oxidative stability, the methods used to analyse and test biodiesel oxidation, as well as the effect that oxidation has on the fuel's properties.
The work reported in this paper details an experimental study of the effects of cooling system hardware changes on diesel engine emissions and fuel economy. Experiments were performed under both steady state and transient conditions and complemented by statistical assessments. Techniques for assessing the thermal integrity of the engine as a consequence of such changes are also presented. An experimental design was constructed to investigate the effect of water pump throttling, coolant flow control through the oil cooler, and the adoption of a pressure resistive thermostat (PRT). Use of these thermal controls offers a useful trade-off between NO x and fuel economy, with a saving of around 3 per cent in b.s.f.c. for a 10 per cent NO x penalty at low load, where NO x output is less of a concern. However, these benefits were not observed during drive cycle testing.
A detailed programme of work has been undertaken to quantify the suitability of predictive methods for accurate determination of the levels of boiling heat transfer within an internal combustion (IC) engine cooling gallery simulator. An extensive array of experimental data has been obtained as the basis for the predictive validation. Working on the principle of superposition, the convective component of heat transfer has been represented by the established Dittus-Boelter correlation which has been extensively modified to account for developing boundary layers, surface roughness and nearwall viscous effects. The boiling component has been represented by the Chen model, modified for binary fluids and subcooling. For the IC engine cooling application it is concluded that the application of the Chen approach must be complemented by a convective heat transfer model that accurately represents the complex thermo-fluid situation being experienced within a developing flow.
Biodiesel is a renewable fuel derived from vegetable, animal, or waste oils. It is synthesized by the transesterification of triglycerides with either methanol or ethanol. The fatty acid profile of biodiesel differs depending upon the feedstock of the derived fuel and is the major factor in determining the properties of the fuel. Using biodiesel blends decreases hydrocarbon, particulate matter, and CO emissions while increasing fuel consumption and NO x emissions. This effect is dependent upon not only the blend ratio but also the fatty acid profile of the biodiesel. Current techniques to determine the fatty acid profile of biodiesel samples are both time-consuming and expensive; however, by measurement of three simple physical properties (viscosity, density, and the refractive index) and a comparison of the values to known standards, it is possible to create a model that can accurately predict both the average chain length and degree of unsaturation.
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