Performance analysis and experimental study of the

Performance analysis and experimental research of electronically controlled CNG engine

I. background

in order to solve the environmental pollution problem and increasingly serious energy problem caused by vehicle engine emissions, countries around the world began to vigorously develop alternative fuel vehicles while formulating various strict vehicle emission regulations to regulate vehicle production and use. Due to the advantages of natural gas in terms of resources and cost, natural gas vehicles have developed rapidly, and the full set of technologies for vehicle refitting, natural gas storage and gas filling stations are becoming more and more mature. Compared with gasoline, natural gas can not only save oil resources and reduce fuel costs, but also greatly reduce environmental pollution as a clean fuel. The development direction of natural gas engine technology is to adopt advanced technologies such as electronically controlled multi-point sequential injection, lean burn closed-loop control and high-energy electronic ignition. Among them, fuel injection, high-energy electronic ignition, lean burn technology and ignition control are the main contents of engine research; It is the basis to ensure the normal operation of natural gas engine and the key to improve its performance in all aspects, so it is necessary to study this aspect

II. Research on performance bench test of electronically controlled CNG engine

test is an important means of engine performance development. In order to explore the control law of electronically controlled CNG engine in fuel injection and ignition, develop lean burn system with excellent performance, and determine the optimal control parameters, a large number of engine bench comparison tests have been carried out. The following is a simple analysis of some bench test results of electronic controlled CNG engine performance

(I) main performance parameters of the test engine

the test model is an electronically controlled supercharged single fuel compressed natural gas engine based on WT615 diesel engine produced by Weifang Diesel Engine Factory. See Table 1 for the main performance indexes and structural parameters of the natural gas engine

(II) injection timing test

the parameters controlled by the electronically controlled natural gas injection system include injection advance angle and injection pulse width. The injection advance angle is the angle from the injection start time to the crankshaft rotation at the top dead center of the intake stroke. The selection of this parameter has a certain impact on the engine performance

in this experiment, adjust the injection delay angle at 1400r/min and 1800r/min respectively, and measure the engine power, gas consumption rate, NOx and HC. The results are shown in Figure 1

1. when the injection delay angle is too large, the power, economy and emission of the engine are significantly reduced. Under low-speed conditions, when the injection delay angle is too large, the economy and power performance of the engine will decline, and the economy will decline significantly

2. At low speed, after the injection delay angle of 400, HC emissions and fuel consumption rate increase sharply, while NOx gradually decreases. This is mainly because the injection delay angle is too large, the fuel combustion is incomplete, the temperature in the cylinder is low, and the power is low. Therefore, HC emissions and fuel consumption rate increase sharply, and NOx gradually decreases. Under high-speed conditions, the emissions of NOx and HC reach the maximum at the delay angle of about 300

3. At the same speed of 1400r/min, when the injection pulse width increases by 0.6ms, as shown in Figure 1 (b), NOx increases sharply, and the power increases by 5kW, while other performance parameters change slightly, indicating that when the injection pulse width is large, the mixture concentration is dense, and the combustion temperature rises sharply, resulting in a large amount of NOx

this natural gas engine is an intake manifold injection mode. Due to the valve overlap angle of a section of intake and exhaust valves opening at the same time, if the injection start time is too early, a part of the mixture enters the exhaust pipe during the scavenging process, which not only increases the consumption of natural gas, but also leads to the deterioration of engine emissions, and the mixture entering the hot exhaust pipe may also burn in the exhaust pipe, raising the temperature of the supercharged exhaust gas. If the injection stop time is later than the closing time of the intake valve, natural gas will accumulate in the intake pipe, which may cause backfire. The engine inlet valve opening time used in this paper is 2 ° before TDC, and the exhaust valve closing time is 5 ° after TDC. According to the analysis of the experimental results and "considering that the injection opening itself has a certain time lag, the natural gas inlet time is positioned at the inlet valve opening time

(III) ignition energy test

in the ignition energy test, 1250r/min and 1400 rpm with high energy efficiency, high quality, high safety and 1800r/min are selected respectively. The ignition energy is from 41 to 400W. The impact on power, HC and CO is analyzed, as shown in Figure 2. From Figure 2, it can be seen that:

1. For the natural gas engine studied in this paper, after the ignition energy is greater than 41mj, The engine can work stably and continue to increase the ignition energy. When the speed is 1400r/min and the throttle opening is 75%, the engine power decreases by 7KW and HC decreases sharply. When the speed is 1400r/min and the throttle opening is 50%, HC has an upward trend

2. under various working conditions, the change of ignition energy has little effect on CO emission and power

3. Under heavy load or high-speed conditions, HC emissions will increase when the ignition energy is small

comprehensive economy, dynamic 2 When focusing, pay attention not to make the objective lens touch the force and emission of the sample. At low speed or low load, the better ignition energy range of natural gas engine is 41 ~ 84mj; Under high load and high speed conditions, the better ignition energy range is 110 ~ 160mj. On this basis, the optimized energization time of ignition primary coil under various working conditions is determined. According to the experimental results, the system controls the energization time of the primary coil to about 5ms, so as to ensure that the ignition energy E of the engine is greater than 140mj

(IV) lean burn test

in the lean burn test, at 1400r/min and 1800r/min, respectively, under partial load, Excess air coefficient (when it changes from 1.2 to 1.65, analyze the influence of power, fuel gas consumption rate, NOx and HC, as shown in Figure 3. From Figure 3, it can be seen that:

1. Lean burn has a significant impact on the economy and power of the engine. When the excess air coefficient is 1.5, the fuel consumption is the lowest and the engine output power is the largest.

2. The excess air coefficient corresponding to the maximum value of no 2 emission is 1.3 ~ 1.4, and with the increase of the excess air coefficient Increase and decrease, mainly because the excess air coefficient increases, the combustion temperature in the cylinder decreases, and then NOx decreases

3.hc emission increases with the increase of excess air coefficient when only c/c composites are considered to be the only one with the allowable ratio above 20. After the excess air coefficient is greater than 1.5, it begins to increase sharply, mainly due to lean combustion and incomplete fuel combustion. Research shows that the main component of HC emissions from natural gas engines is unburned methane, which is difficult to oxidize due to its high combustion temperature

III. summary

1. From the data analysis of injection timing test, it can be seen that when the injection delay angle is too large, the engine power decreases, HC emissions increase, and fuel consumption rate increases, so the injection delay angle of the engine should be smaller

2. In terms of economy, power and emission, on the premise of meeting the stable operation of the engine at low speed or low load, the better ignition energy of natural gas engine is smaller, and the better ignition energy is larger at high load and high speed

3. From the test results, it can be seen that the best excess air coefficient is about 1.5. (end)