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Diesel engine has widely been used in the non-road mobile machinery industry, because of its considerable advantages in power, economy, and reliability. However, the working process of an diesel engine is rough, due mainly to the compression ignition operating mode Furthermore, the noise of the diesel engine cannot meet the requirements of living comfort. Therefore, it is highly necessary to reduce the noise of diesel engines. The noise of the internal combustion engine mainly includes aerodynamic, mechanical, and combustion noise. Combustion noise plays a leading role in the total noise of diesel engines, especially for direct injection diesel engines. Combustion noise is also closely related to the combustion process of internal combustion engines. The combustion noise is greater, as the combustion process is more intense in recent years. Fortunately, the noise can be reduced via the optimized parameters and tunable process. Therefore, the in-cylinder combustion process can also be optimized for the noise reduction of diesel engines. Since the pre-injection, exhaust gas recirculation (EGR), and turbocharging technologies cannot be widely used to reduce combustion noise for low power non-road diesel engines, due to the cost, structure, and application object. Therefore, the reasonable selection of parameters can make the matching of "fuel, air, and chamber" more perfect on the basis of existing low-power non-road diesel engine parts, thereby improving the combustion process in the cylinder. In this study, an optimization experiment was performed on the in-cylinder combustion of a diesel engine, in order to ensure the power performance, economy, NOx, and soot emissions of low power non-road machinery, while reducing the combustion noise in the diesel engine. A low-power non-road 4D29G31 diesel engine was used as an original engine. The optimization was made on the nozzle protrusion, nozzle hole number, nozzle hole diameter, and swirl ratio. The “fuel, air, and chamber” achieved the best matching state to improve the fuel-air mixing, the combustion in cylinder, and performance of diesel engine. The dynamic fuel supply advance angle was optimized to shorter the ignition delay time. The combustion rate and pressure oscillations were then be suppressed during the rapid combustion period. The maximum combustion pressure and the rising rate of the diesel engine under the rated condition were reduced by 18% and 44.9% after optimization, respectively, where the noise of the engine was reduced by 0.73 dB, compared with the original engine. The maximum combustion pressure and the rising rate of the diesel engine were reduced by 39% and 40% under the maximum torque condition, respectively, where the noise of the engine was reduced by 1.07 dB than before. It demonstrated that the combustion noise was reduced significantly in the whole diesel engine after optimization. At the same time, the economy and emission performance of diesel engines reached optimal in a low-power non-road diesel engine. [ABSTRACT FROM AUTHOR]

As society and economy developing, the problem caused by non-road diesel engine emission has been widely drawing people’s attention. Increasingly serious environmental problems have forced people to use advanced technology to reduce engine emissions and lots of countries have established non-road diesel engine emission regulations. Developed countries, represented by the United States of America and the European Union, have formulated stringent emission regulations to limit emissions from non-road diesel engines. China issued the limits and measurement methods for exhaust pollutants from diesel engines of non-road mobile machinery in 2014. By using the vehicle emission control technology, the high power (>37 kW) diesel engine could meet the emission standards. Because of the structure, production costs and application limit, electronic control system, common rail system, turbocharger, exhaust gas recirculation and selective catalytic reduction can’t be applied in low power (<37 kW) non-road diesel engine. So there are a lot of technical difficulties for the upgrade of low power non-road diesel engine emissions. In addition, the strict regulations on the brake specific fuel consumption (BSFC) of diesel engines were made, which further increases the difficulty of such diesel engine emissions meeting the requirements. The emission standards implementation and requirements of the low power non-road diesel engine are constantly tightened. The electronically controlled VE pump-line-nozzle fuel injection system has the advantages of low cost, simple structure, convenient arrangement on the engine, and also has the potential to meet Level III or even Level IV emission regulation requirements in China. Therefore, it’s necessary to research and develop a low power non-road diesel engine with high performances and low emissions. In this article, the non-road N490 direct injection diesel engine was taken as the prototype, By using a combination of theoretical analysis and experimental research, technology strategy of low non-road diesel engines was explored to meet the requirements of high performance and low emissions. By increasing the pump cam lift, reducing the inner diameter of the high-pressure fuel pipe, and improving nozzle geometry of the injector, the maximum nozzle side pressures at the rated condition and the maximum torque condition increased by 32.7% and 50%, respectively. Re-entrant dumbbell-shaped chamber was designed to strengthen the central bulge of the combustion chamber bottom, which improved the air movement in the combustion chamber. By adjusting the valve timing, the volumetric efficiency of the diesel engine was improved. The combustion was optimized by reducing the fuel injection quantity during ignition delay period. After optimizing the parameters of the fuel injection system, the valve timing and combustion chamber, the diesel engine performance was greatly improved. Compared with the original engine, both at the rated condition and at the maximum torque condition, the specific fuel consumption was decreased by 3.0% and 2.43%, respectively, and the light-proof smoke was also decreased by 14.6% and 10%, respectively. The experimental results showed that the exhaust emissions of carbon monoxide (CO), nitrogen oxide (NOx) + hydrocarbon (HC), and particulate matter (PM) were 1.109, 6.23 and 0.522 g/(kW·h), respectively, which were lower than Level emission standards in China. Compared with the results of the prototype, the measured values of CO, NOx+HC and PM were reduced by 34.7%, 21.5% and 34.9%, respectively. At the same time, both the maximum cylinder pressure and the heat release rate were greatly reduced. At the rated and the maximum torque conditions, the maximum cylinder pressures were decreased by 15.8% and 9.6%, respectively; the maximum heat release rates were decreased by 9% and 8.8%, respectively. Through the analysis of experimental data, the research shows that optimization matching of fuel injection, in-cylinder air movement and combustion chamber can not only decrease the exhaust emissions obviously but improve the fuel economy of the engine. [ABSTRACT FROM AUTHOR]

The huge annual output of single-cylinder diesel engines is a major feature of Chinese internal combustion engine industry. In China the amount of these engines with bore diameter below 80 mm accounts for 35% of domestic production. Most of these diesel engines adopt the swirl chamber combustion system. However, with the development of direct-injection process, many problems for these engines occur, such as large smoke emissions at full load, poor performance under low speed and high idle speed, and there are few basic researches on them. Therefore, the research of low-emission high-performance swirl chamber diesel engines contains certain academic significance and practical value. The 170F swirl chamber diesel engine was used as the research prototype, and with the method of experiment and numerical simulation, the fuel injection and combustion systems were analyzed. By the design of new injector, the establishment of simulation model of injection system and the optimization of the injection parameters, the maximum fuel pressure under the rated conditions increased from 18.54 to 25.28 MPa, the initial injection rate reduced and the shape of injection rate was optimized. By the simulation of combustion with the software FIRE, the deviate distance from the injection oil line to the center of the swirl chamber and the best volume ratio were determined. The results showed that when the deviate distance from the injection oil line to the center of the swirl chamber was at 0.33-0.38 R (R is the radius of the swirl chamber), and the volume ratio was in the range of 0.47-0.50, the mixing and combustion performance would be better. This study showed that in order to achieve the targets of low emissions and high performance, the injection parameters and performances of the swirl chamber diesel engine should be designed and optimized according to its displacement just similar with the direct-injection diesel engine. The test results of 170F swirl chamber diesel engine showed that the brake specific fuel consumption (BSFC) of the original engine under the rated condition (2.6 kW, 3 000 r/min) was 327.3 g/(kW·h) and the smoke was 4.5 BSU. When the long-size short-structure nozzle was used and the fuel injection system was optimized, the BSFC and the smoke decreased to 282.2 g/(kW·h) and 2.0 BSU respectively. After the parameters of the combustion system were matched, the BSFC and the smoke dropped to 274.7 g/(kW·h) and 1.2 BSU respectively. The experimental results showed that the specific emissions of the optimized diesel were lower than the emission standards in Phase Ⅲ in China. Compared with results of the original engine, the CO and HC+NOX emissions decreased by 70.3% and 20.9% respectively under the 5 conditions. Moreover, the CO and HC+NOX emissions decreased by 72.8% and 21.3% respectively under the 8 conditions. The BSFC decreased by 16% and the diesel smoke was reduced from 4.5 to 1.2 BSU under the rated condition. The research provides a technology route of energy-saving and emission-reduction for swirl chamber diesel engines. [ABSTRACT FROM AUTHOR]