A six cylinder, two stroke/cycle diesel engine is 83% efficient and has a cylinder constant of 0.998 while operating with a mean effective pressure of 15 kg/cm² at a speed of 100 RPM. What is the metric brake horse power developed?
• Use the metric brake horsepower (mbhp) formula that involves mean effective pressure, cylinder constant, RPM, and mechanical efficiency. • Understand what the cylinder constant represents and how it already combines several geometric and unit-conversion factors. • Remember that two-stroke engines have a power stroke every revolution, which affects how RPM is used compared to four-stroke engines.
• First, compute the indicated power using mean effective pressure, cylinder constant, engine speed, and number of cylinders. Then apply the given efficiency to get brake power. • Ask yourself: does the cylinder constant given already include the effect of the number of cylinders, or do you need to multiply by the number of cylinders separately? • Check how the 83% efficiency is applied: is it used to increase or decrease the indicated power to get brake power?
• Confirm whether the formula you use is consistent with a two-stroke, not a four-stroke, engine (i.e., power strokes per revolution). • Verify that you are correctly interpreting 0.998 as the cylinder constant per cylinder, then multiplying by the number of cylinders (6). • After calculating, compare your mbhp value to the choices and see which one is closest, making sure you haven’t forgotten to multiply by efficiency (0.83).
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