Combustion technology
In the most significant fuel injection systems with improved combustion effects, "high pressure injection" and "degree of freedom of injection" have become an important means of the current fuel injection system. The common-rail fuel injection system has entered the second generation. In the variable injection period of 180° CA or more, the injection pressure of 160-180 MPa and five multi-stage injections can be achieved. In the future, high-pressure injection of more than 200 MPa is expected to be achieved through measures such as increasing the strength of various parts of the common-rail injection system and reducing the amount of oil leakage. In the future, methods such as premixed combustion and low NOx combustion are improved. In order to realize premixed combustion, measures such as multi-stage injection and switching combustion that promote premixing are used, and higher degrees of freedom of injection are required. In addition, due to the high EGR and low NOx combustion, it is necessary to consider further increasing the injection pressure as a countermeasure against black smoke in the state where the O2 concentration in the intake air is greatly reduced. On the other hand, the combination of the fuel injection system and the post-processing technology is also important. The NOx adsorption-reduction catalyst needs a different post injection mode than the DPF. While enhancing the freedom of injection and high-pressure injection, it is expected that concepts such as “change in combustion method†and “combination with post-processing†will be added to new keywords. To control compression ignition fire of uniform premix gas, it is necessary to control the pre-ignition temperature history of the chemical reaction controlling the oxidation of fuel and the extremely difficult physical quantities such as the gas composition and heat capacity in the cylinder, and it is expected that the sensor must be made on an unprecedented scale. The computational power of the control unit is practical. The "premixed combustion" proposed by Shinmoto et al. avoided the combustion of NOx and soot on the flame temperature and equivalence ratio (T-Φ) maps to achieve ultra-low emissions. In addition, the increase in thermal efficiency is also an important factor. The concept of "clean diesel engine combustion" proposed by the US Environmental Protection Agency (EPA) and the "ACTION" concept proposed by Ricardo Research Institute in the UK are to reduce the O2 concentration in the cylinder to 11% to 14%, and achieve reduction of NOx without reducing the combustion efficiency. 90% of emissions. In order to realize this idea, it is necessary to take into consideration the technologies of low compression ratio, two-stage supercharging, electric compressor, and low-pressure loop (LPL) EGR without increasing the fuel consumption while taking into account the supercharging and high EGR. It is EGR+air volume control and the mixing of fuel and air to suppress soot formation. On the other hand, the premixed diesel engine combustion is a combustion system in which the fuel injection period and the combustion period do not overlap with each other and the diffusion combustion is not caused (ie, non-homogeneous). Fuel injection is performed earlier before TDC, or fuel injection is performed during the expansion stroke to ensure sufficient ignition delay. The potential for emission reduction is great.
The variable technique of the intake valve closing timing and the negative overlap of the top dead center valves in the exhaust and intake strokes can control the residual exhaust gas, attracting attention as a condition for suppressing deterioration of the thermal efficiency and directly controlling the premixed combustion. Attempts have been made to intentionally create a non-uniform field at the pre-combustion temperature or mixture concentration to suppress the exothermic peak.
Pressurization technology
In addition to seeking to increase the flow range of the compressor to increase the efficiency, the supercharging technology also uses a bleed valve in order to meet the high torque and high power of the engine. The actual vehicle also uses a variable section turbocharger (VGT). Using the EGR valve and VGT to achieve simultaneous control of the intake air amount and the EGR rate technology together with the high-pressure fuel injection technology becomes the mainstream technology for reducing emissions. From the emission limits of Japan's new long-term emission regulations in 2009 and the US 2010 emission regulations, NOx emissions must be reduced and EGR will become a more important technology. To increase the EGR rate, to ensure the driving force of the compressor, it is also required that the turbine must have a higher efficiency and at the same time must further increase the pressure ratio and formulate surging measures. In some high-power engines, two-stage boosting is also considered. With the increase of the heat release of cooling EGR and the increase of heat release of high-pressure intercoolers, the improvement of cooling technology is imperative. Need to reduce the friction caused by ball bearings, etc., while the use of titanium alloy impeller to achieve high efficiency and high pressure ratio, low inertia and other research. In the transitional operating conditions as a means to supplement the lack of air, measures such as electric compressors and electric turbochargers may be used.
The future of NOx reduction catalysts
Sulfur poisoning of NOx adsorption and reduction catalyst due to sulphur in light oil, and desulfurization treatment process for removing sulfate regularly is necessary. In Japan, low-sulfur fuels with a sulfur content of less than 10×10-6 can now be used, and DPNR systems have been used in commercial vehicles. As the NOx reducing agent that decomposes and reduces the adsorption, CO and H2 are more effective than hydrocarbons such as light oil. A NOx adsorption and reduction system using a fuel reformer that generates H2 and CO from light oil, raises the temperature by the oxidation reaction, and generates H2 and CO in a rich gas (oxygen-free state) environment. The device must raise the temperature to the combustion temperature of the catalyst, so its warming response has also become a subject of research. If the light oil can catch fire at low temperature, the NOx reduction rate in the low temperature area will be greatly improved. The practical application of the SCR system using less toxic urea water as a reducing agent has been continuously developed. In addition to zeolite-based catalysts, SCR catalysts are also researching the use of molded vanadium-based catalysts, but toxic noble metals such as vanadium, the stability at high temperatures will be reduced, the zeolite-based catalysts in Japan have practical applications, SCR system injection of urea water In the process of producing ammonia, there may be a problem of generation of by-products, and it is necessary to confirm whether there is any substance that is not specified in the exhaust gas due to urea emission regulations.
DPF system
In order to improve the DPF's PM trapping performance, countermeasures such as making the pore structure denser and reducing the exhaust gas flow rate through the filter have been taken. However, its negative effect is the increase in pressure loss. For this reason, honeycomb-like surface filtration methods are being studied, and deep-filtering DPF systems are being explored. To increase DPF regeneration efficiency, consider using a dedicated heat source. In addition, attention has been paid to a method of bypassing exhaust gas (a plurality of parallel-arranged DPF switching methods) that does not pass all the exhaust gas. DPF regeneration using low-temperature plasma is under investigation and it is possible to achieve high-efficiency regeneration under full airflow conditions. Integrating DPF and NOx post-processing devices effectively and achieving miniaturization is critical. The DPNR system incorporating the NOx adsorption reduction catalyst in the DPF is an option.
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