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84 Victor Pantilie et al. industrial research. The simulation program used in the present paper is AVL Boost v2011. The modelling was made for the DOHC Daewoo engine (aspirated engine and supercharged engine) with the characteristics from Table 2. The combustion law used was the Vibe law for two zones and the heat transfer coefficient used was Woschni. Table 2 Engine specifications Engine type DOHC Displacement 1.5, litres Stroke 81.5, mm Bore 76.5, mm Cylinders 4 Number of valves 16 Connecting rod length 120, mm Compression ratio 9.2 Maximum power engine speed 4800, rpm Engine operating regimes: full load and 3500 rpm with the next supercharge pressure and excess air-fuel ratio: gasoline with normal intake at λ=0.8, 0.85, 0.9, 1; gasoline with supercharge pressure 1.3 at λ=0.8, 0.85, 0.9; gasoline with supercharge pressure 1.5 λ=0.8, 0.85, 0.9; hydrogen with normal intake at λ=1, 1.2, 1.3, 1.5, 2, 2.5; hydrogen with supercharge pressure 1.3 at λ=1, 1.3, 1.4, 1.5, 2, 2.5; hydrogen with supercharge pressure 1.5 at λ=1, 1.4, 1.5, 2, 2.5; For each simulation were made 50 cycles for better results. Supercharging the engine prevent backfire, cools the cylinder walls and increases the engine performance, allowing hydrogen to be used in safe conditions and with lower pollutant emissions. To protect the engine against damage the supercharge pressure was limited to 1.5 bar. 3. Results For the engine running on gasoline with normal intake the maximum pressure is 48 bar. When the engine is supercharged the pressure increases significantly reaching 87 bar with a supercharge pressure of 1.5 bar. Using hydrogen as a fuel, the maximum pressure with normal intake is higher at stoichiometric excess air-fuel ratio and as the dosage was leaner the pressure drops at 43 bar at excess air-fuel ratio equal to 2.5. To achieve similar performance as with gasoline (normal intake), the engine running on hydrogen is supercharged and for the reduction of the NOx emissions, the values for the excess air-fuel ratio should be greater than 1.8. The supercharge pressure used is
Bul. Inst. Polit. Iaşi, t. LVIII (LXII), f. 4, 2012 85 1.3 bar and 1.5 bar. Maximum pressure reached when using supercharged hydrogen is around 89 bar at stoichiometric excess air-fuel ratio (Fig. 1). Fig. 1 – Maximum pressure diagram. The maximum temperatures when using gasoline presents a slight increase as the engine was supercharged and as the excess air-fuel ratio increased from 0.8 to 0.9 (Fig. 2). On hydrogen the excess air-fuel ratio has a major impact so the maximum temperatures reached 2900 K when the engine is supercharged at 1.5 bar at stoichiometric excess air-fuel ratio and dropped below 1900 K at leaner dosage (λ=2.5). Fig. 2 – Maximum temperature diagram. The brake specific fuel consumption is much lower at the use of hydrogen due to good hydrogen burning proprieties and heat losses reduction. A slight impact on BSFC has also the supercharge pressure, and it can be seen in the figure below that when the engine is supercharged the BSFC decreases on gasoline as well as on hydrogen.
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BULETINUL INSTITUTULUI POLITEHNIC D
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