In this paper, an experimental study was conducted to enhance the thermal performance of a double-pass solar air heater (SAH) using phase change material (PCM) for thermal storage at climatic conditions of Baghdad city -Iraq. The double-pass solar air heater integrated with thermal storage system was manufactured and tested to ensure that the air heating reserved after the absence of the sun. The rectangular cavity filled with paraffin wax was used as a latent heat storage and incorporated into the lower channel of solar air heater. Experiments were carried out to evaluate the charging and discharging characteristics of two similar designed solar air collectors with and without using phase change material at a constant air mass flow rate of (0.0375 kg/sec). The parameters that affect the thermal performance of the SAH with and without the PCMs presented by solar radiation, the difference in air temperature, outlet air temperature, instantaneous thermal efficiency, and daily efficiency are evaluated. The experimental results show that when using the PCM, the temperature of the outlet air was enhanced and increased over the ambient temperature by (1.5 -6.5 °C) after sunset for 5 hours period. It was found that the instantaneous thermal efficiency of the heater using thermal storage exceeds 100% after sunset, this is due to a large amount of heat stored in the paraffin wax that has been released during the discharge process. Also, it was found that the daily efficiency of the double pass SAH integrated with and without thermal energy storage unit was (56, 47%) respectively.

The aim of this paper is to study the effect of changing the compression ratio on the performance and emission characteristics of single cylinder, 4-stroke compression ignition (CI) engine running with biodiesel and pure diesel fuel. Corn oil biodiesel blends were prepared viz. B5(5 %), B10 (10 %), B1 (15 %) and B20 (20 %) (by volume). The tests were performed at full load, constant speed 1500 rpm and different compression ratios 14, 15, 16, 17 and 18 %. The engine performance like brake thermal efficiency (BTE), brake specific fuel consumption (BSFC) and emissions of CO, CO2, HC, NOX and smoke opacity for all biodiesel blends were measured. The results showed that on increasing the compression ratios, the BTE increases and BSFC decrease for all types of fuel used, but it was found that for biodiesel blends B5, B10, B15 and B20, the BTE slightly decreased by 2, 4.2, 6.5 and 8.3 % and the BSFC increased by 3.3, 6.3, 9.4 and 13 % respectively, compared to the pure diesel fuel due to the high viscosity and density of biodiesel. With increasing the compression ratio and proportion of biodiesel blend, the emissions of CO, HC and smoke opacity were decreased, at the same time, the CO2 and NOX emissions were increased. The highest reduction in the emissions of CO, HC and smoke was found in the B20 biodiesel blend, which was 30, 26 and 23.8 %, respectively, while the same blend showed the highest increase in emissions of CO2 and NOX, which were 21 and 25.7 % respectively, compared to pure diesel fuel. Therefore, the biodiesel blend can be used at proportion up to 20 % and blend with diesel fuel in CI engines without any modifications.

Enhancement of heat transfer in the tube heat exchanger is studied experimentally by using discrete twisted tapes. Three different positions were selected for inserting turbulators along tube section (horizontal position by α= 00, inclined position by α= 45 0 and vertical position by α= 900). The space between turbulators was fixed by distributing 5 pieces of these turbulators with pitch ratio    PR = (0.44). Also, the factor of constant heat flux was applied as a boundary condition around the tube test section for all experiments of this investigation, while the flow rates were selected as a variable factor (Reynolds number values vary from 5000 to 15000). The results show that using discrete twisted tapes enhances the heat transfer rate by about 60.7-103.7 % compared with plane tube case. Also, inserting turbulators with inclined position offers maximum heat transfer rate by 103.7%.

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Environmentally friend biodiesel fuel from corn oil was tested in single-cylinder 4-stroke diesel engine operated. Three blends of fuels were prepared from corn oil and diesel fuel viz. 7, 15, and 20 % (designated as B7, B15, and B20, respectively). Tests were conducted on this engine using these blends at a constant speed (1500 rpm) and varying loads (0 % to 100 %). The emissions of carbon monoxide, carbon dioxide, unburned hydrocarbons, nitrogen oxides (NOX) and smoke opacity were measured. In all engine loads, results showed that the emission of CO, HC, and smoke emissions were reduced, while that of NOX and CO2 were increased. Biodiesel blend (B20) showed the highest decrease of the CO and HC and smoke emissions by 22.13 %, 18.5 %, and 25.8 % respectively. While that of NOX and CO2 emissions were increased by 22.3 % and 22%, respectively. It can be recommended as a sound environment friend and renewable for use in diesel engines and can be used without any significant modifications in the engine design.