top of page # Creating a Vignette Group

Public·1 student

Although the engine experiments are designed more and more realistic in recent time, there is still some distance between test results to the real application. In addition, the traditional two-stroke engine test stations are always designed more suitable for the ground vehicles because the test torque is always added by means of electromagnetism, which is hard to test the output power of an aeroengine with a propeller. Furthermore, in order to get accurate results, the experiment conditions have to be prepared strictly such as high precision sensors and stable environment, which will greatly increase the research cost. Last but not the least, it is dangerous and inaccurate to simulate extreme working conditions by engine station tests.

The engine working process is designed, as shown in Figure 3, according to the working principle of the one-dimensional simulation software GT-Power. In this picture, it can be seen that connected to the inlet port there are two symmetrical crankcase chambers with numbers 1 and 2. When the air-fuel mixture is flows into the crankcase, it is generally assumed that two homogeneous mounts of oil and gas are divided by the crankshaft and then flow into the two cylinders. Furthermore, there are also symmetrical scavenging passages, intake ports, cylinder chambers, exhaust ports, and exhaust passages. The opening and closing degrees of the two kinds of ports determine the intake time of the air-fuel mixture and the exhaust time of the emissions. According to the actual measurement results, the opening areas with the crankshaft angles are as shown in Figures 4(a) and 4(b). It should be noted that, in these figures, range of the x-coordinates is 0 to 180 degrees which is in the first working stroke. The changing area with the shaft angle is symmetrical in the second working stroke.

Then, the one-dimensional GT-Power model of the two-stroke aeroengine can be set, as shown in Figure 5, according to the aeroengine working process. Structure of the aeroengine is based on the actual measure results.

Main setting parameters of the fuel injector are ṁf and the set air-fuel ratio (λset). In practice, ECU controls the injector work and breaks through pulse signal with a certain width. Relationship between , λset, and the inject fuel pulse width (Pw) is shown in the following equation:where is volumetric efficiency, ρref is reference air density used to calculate volumetric efficiency, VD is the engine displacement, and #CYL is the number of cylinders. From this equation, we can see that Pw directly determines the injected fuel flow. In order to improve the comprehensive performance of the aeroengine, the inject fuel flow rates are calibrated under different working conditions. So, as to make the setup more intuitive, in this paper, the calibrating standard is based on the expected air-fuel ratio, and then the ECU can calculate the output Pw in the real practice. However, because the injector is driven by electromagnetic force, the dynamic action of the needle valve should be considered in the compensation of the set pulse width.

Propeller load can be calculated according to different working conditions based on standard strip analysis. As known from the calculation, load torque of the propeller mainly depends on engine speed (n) and propeller rotor diameter (rp). Main formula of the torque is as follows:where MR is the propeller torque, ΔD is differential form of the drag force, ΔL is differential form of the lift force, β is the intake air flow angle, and rp is the propeller radius. Then, the parameters are confirmed according to a blade material; then, we can get the torque MAP in horizontal direction under different working conditions, which is shown in Figure 8. From Figure 8, we can see that the load torque does not increase linearly with increasing engine speed and the UAV propeller rotor diameter. However, we can substitute the torque MAP into the one-dimensional model by the linear interpolation method.

As shown in Figures 12 and 13, it can be seen that when the throttle opening degree is constant, the output torque curves, and output power curves will have a peak at a same speed. However, it is difficult to find a regular rule between the set AFR and these two output characteristics. That is because when the throttle opening degree is set constantly, there must be a primal AFR setting value with different working conditions which is in accordance with the engine external characteristics. According to the settled weight, the optimization should be comprehensively considered. In addition, from the two figures, the curve trends are almost the same, so only one of the items can be considered when setting weights in order to reduce the amount of calculation. 350c69d7ab