Investigation of extracted Sclerocarya birrea seed oil as a bioenergy resource for compression ignition engines

Sclerocarya birrea(Marula)seed oil was extracted and characterized for its physico-chemical properties and fatty acid compositions,respectively,by using standardized laboratory methods of the Association of Official and Analytical Chemist(AOAC).The fuel and lubrication properties of marula oil were also determined by using the ASTM methods,and the oil was evaluated in terms of its antiwear,viscometrics,volatility,stability,environmental compatibility properties and energy content.It was found that the high percentage of mono-unsaturated oleic acid(73.6%)provided the oiliness that makes marula oil a natural alternative to genetically modify high oleic acid sunflower oil used in biodiesel production.The aggregate properties of seed oiliness as exemplified by the high oleic acid content,high saponification value(178.6 mg/KOH)and viscosity(41 mm2/s)makes marula oil to be prospective based oil for engine crank case biolubricants with antiwear and friction reduction properties.However,the higher oil viscosity exhibited by marula seed oil in comparison to diesel could pose some durability problems to compression ignition engines,when used directly as fuel.Nonetheless,the reduction of oil viscosity would be required by heating,blending with diesel fuel,or by transesterification to forestall the risk of engine failure resulting from the use of unmodified marula oil.The flash point of marula oil(235℃)is somewhat close to that of monograde SAE 40 mineral oil(240℃),and appreciably higher than that of diesel fuel(52℃).The high flash point makes the seed oil less flammable and ensures safer handling and transportation.While,the low pour point(-13.7℃)ensures the oil usability for engines at cold start and under low load conditions.The oxidation stability of marula oil is ascribed to the traces of natural antioxidants presented in the oil and improves the oil’s shelf life,notwithstanding the high peroxide value(4.58 mequiv/kg),and linolenic acid content(0.3%),which ought to have been the culprit for lipolytic hydrolysis and rancidity.Furthermore,marula seed oil is more biodegradable and environmentally friendly than oils derived from petroleum crude.The closely related cetane number(47.8)and heating values(38.2 mJ/kg)of marula oil to diesel fuel would undeniably sustain the combustion efficiency of diesel fuel and also supply a comparable engine performance output in compression ignition engines.The candidacy of marula seed oil,as a bioenergy resource for alternative fuel,fuel additives and lubricants,will no doubt expand the energy supply mix,conserve fossil fuel reserves and mitigate environmental contamination.

Real-time Control Oriented HCCI Engine Cycle-to-cycle Dynamic Modelling

For homogeneous charge compression ignition （HCCI） combustion, the auto-ignition process is very sensitive to in-cylinder conditions, including in-cylinder temperature, in-cylinder components and concentrations. Therefore, accurate control is required for reliable and efficient HCCI combustion. This paper outlines a simplified gasoline-fueled HCCI engine model implemented in Simulink environment. The model is able to run in real-time and with fixed simulation steps with the aim of cycle-to-cycle control and hardware- in-the-loop simulation. With the aim of controlling the desired amount of the trapped exhaust gas recirculation （EGR） from the previous cycle, the phase of the intake and exhaust valves and the respective profiles are designed to vary in this model. The model is able to anticipate the auto-ignition timing and the in-cylinder pressure and temperature. The validation has been conducted using a comparison of the experimental results on Ricardo Hydro engine published in a research by Tianjin University and a JAGUAR V6 HCCI test engine at the University of Birmingham. The comparison shows the typical HCCI combustion and a fair agreement between the simulation and experimental results.

Effect of dicarboxylic acid esters on the lubricity of aviation kerosene for use in CI engines

To reduce their fuel related logistic burden,North Atlantic Treaty Organization(NATO)Armed Forces are advancing the use of a single fuel for both aircraft and ground equipment.To this end,F-34(the commercial equivalent is Jet A-1)is replacing distillate diesel fuel in many applications.However,tests conducted with this kerosene type on high frequency reciprocating rig showed that this type of fuel causes unacceptable wear.This excessive wear is caused by the poor lubricity of aviation fuel.In order to make this type of fuel compatible with direct injection compression engines,seven di-carboxylic acid esters have tested to improve the lubricity of kerosene.Tribological results showed that all esters tested in this series of experiments seem to be suitable for increasing the kerosene lubricity to a satisfactory level.