A Primary Design Example of Turbocharged Zhou Engine Vs. Wartsila 12V32
The Wartsila 32 is very famous turbocharged four-stroke diesel engine. Here, we will design a turbocharged Zhou Engine to realize the power of Wartsila 12V32,to show the unique characteristic of Zhou Engine.
According to“Wartsila 32 Product Guide”, the Wartsila 12V32: using of the fuel of HFO (Heavy Fuel Oil) or MDF (Marine Diesel Fuel), power 6000kW, rotate speed 750 r/m, four-stroke, 12 cylinders, cylinder bore 320mm, stroke length 400mm, weight 59t, over all dimension 7620*3029*4460mm.
Based on those above data, we draw the piston motion curve of Wartsila 12V32 in fig. 1. The ideal burning time is within the interval of -20° to +20°around the top dead center of the piston, which takes 8.8ms. The fuel of HFO (Heavy Fuel Oil) and MDF (Marine Diesel Fuel), burns slowly, and needs longer burning time than other fuels. This burning time needed limits the rotate speed of this 12V32.
To understand the following content easier, please first read the post “Turbocharged Zhou Engine”.
We design a Zhou Engine that uses the fuel of HFO and MDF, want the working cycle shorter than Wartsila 12V32. We first draw the piston motion curve of this Zhou Engine and show in the fig. 2. We reserve combustion period 15ms, which is longer than the ideal burning time of the 12V32, shown in fig. 1. The working cycle is 40ms. The periods of intake stroke and exhaust stroke are both 8ms, equal the 1/5 of the working cycle. We set this Zhou Engine has six pairs of cylinders; the phase difference between their neighboring cylinders is 1/6 of the working cycle. Therefore, the period of exhaust stroke is longer than the phase difference, we can set the whole exhaust flow has no pulsation. Likewise, we can do so on the whole intake flow.
For easy description, we use the following symbols in table 1, in the following expressions.
We draw the pV-diagram of this turbocharged Zhou Engine, shown in fig. 3. Then calculated, the ideal thermal efficiency is 0.74. According to the example 2 of “A common mistake in textbook of physics”, we estimate that the difference between the ideal and the real thermal efficiency of this turbocharged Zhou Engine ought to be less than 0.10 or 10%. So, the real thermal efficiency of this turbocharged Zhou Engine ought to be higher than 0.64 or 64%.
Then, we draw “the matching diagram of this Zhou Engine and turbocharger” and show in fig. 4. The point G is the shaft of the turbocharger, which ideal output power is 0.5258*F1(MW). The point H is the shaft of the Zhou Engine, which ideal output power is 0.4134*F1(MW). The total ideal output power of the both shafts is (0.5258+0.4134)*F1=0.9392*F1(MW). Here, we set the real thermal efficiency is 0.6 rather than 0.74, set the real output power the both shafts is 0.9392*F1/0.74*0.6=0.7612*F1(MW). If we want to get real output 6000kW=6MW, we need intake fresh air flow rate F1=6/0.7612=7.883m^3/s. If the working cycle frequency of this Zhou Engine is 1500 times/min, then the intake fresh air volume of each working cycle (at Point A) V1=7.883/(1500/60)=0.3153m^3, the volume of the intake and exhaust in each working cycle of this Zhou Engine (at point F and E) is 0.3106*V1=0.097932m^3=97.932L. Here, we set 6 pairs of cylinders, each cylinder with 210mm bore and 236mm stroke length. The real volume of the intake and exhaust in each working cycle is 98.090L. We choose the barrel type of Zhou Engine, reference the post of "Barrel Type of Zhou Engine". The estimated overall dimension of this Zhou Engine is a cylinder with 750mm diameter and 2360mm long. This overall dimension is far smaller than the Wartsila 12V32.
(If we add intercooling inside the dynamic compressor of the fig. 4, we will obtain higher thermal efficiency.)
If you doubt above result, you can calculate all above data again.
For more about Zhou Engine, please see "About Zhou Engine".