Search Results

Exhaust gas recirculation (EGR) is widely used in diesel engines to reduce nitrogen oxide emissions. To meet the strict emission regulations, e.g., Real Driving Emissions, the EGR system is required to be used at temperatures lower than the present ones. However, under cool conditions, an adhesive deposit forms on the EGR valve or cooler because of the particulate matter and other components present in the diesel exhaust. This causes sticking of the EGR valve or degradation of the heat-exchange performance, which are serious problems. In this study, the EGR deposit formation mechanism was investigated based on spatially- and time-resolved scanning electron microscopy (SEM) observation. The deposit was formed in a custom-made sample line using real exhaust emitted from a diesel engine. The exhaust including soot was introduced into the sample line for 24 h (maximum duration), and the formed deposit was observed using SEM.

Mankind developed and enjoyed the automobile civilization, and has lauded the prosperity that it brought about. Commercial vehicle launched the heavy duty diesel engine have been contributing by main transportation system for development of society in the world. However both the local and global environment issues appear depend on the life of mankind, in the world. Especially, global warming is the most stringent issue for our life on the earth. We human beings must lay our existence on the line, and call upon expertise to create solutions for this situation. Diesel engine has great potential for the global warming compatibility by it's high thermal efficiency and diesel vehicle is expected to conserve the environment and to improve the fuel saving for keeping resources in the world. This paper introduces the surrounding of the automobile, such as exhaust emission regulation for heavy duty diesel vehicle, amount and contribution of CO2 emission and noise.

The active regeneration method of a DPF system wherein fuel is supplied to a pre-catalyst with post-injection to cause filter heat-up, was described in previous reports. To succeed in the active regeneration, a pre-catalyst must have high fuel combustion performance at low temperature. Platinum (Pt) had been used as active species of the pre-catalyst. This conventional catalyst was improved by the addition of Palladium (Pd). Fundamental experiments for the catalyst have shown that Pd is very effective for fuel combustion and optimization of the ratio of Pd to Pt causes enhanced NO2 formation to contribute to lengthen the interval between active regenerations. The high performance and enough heat resistance of the newly developed pre-catalyst have been confirmed by engine test.

In order to meet increasingly strict PM legislation, diesel particulate filter systems (DPF) with a conversion rate of about 90% particulate matter (PM) are an essential after-treatment technology. Recently a filtering method using a catalyst has been proposed, which is called the “Continuously Regenerating DPF System[1],” and one can expect a significant degree of system simplification and cost reduction. In the previous report [2] basic characteristics about this continuously regenerating DPF were investigated. Results showed that in city mode driving, where exhaust temperatures are relatively low, continuous regeneration did not occur. Therefore, to “Continuously Regenerating DPF System,” active regeneration control system to oxidize and remove PM is necessary[3]. Then DPF system with higher reliability and active regeneration control method was proposed.

An after-treatment system consisting of a lean NOx trap, diesel particulate filter (DPF), and diesel oxidation catalyst (DOC) was applied to a light-duty commercial vehicle engine. Extensive exhaust gas testing under the transient JE05 test cycle was carried out. Lean NOx trap characteristics and issues related to transient operation were clarified and areas for system improvement were suggested. When exhaust gas temperatures were low, the NOx conversion efficiency was low, then stored NOx remained in the catalyst during rich operation, without desorption and reduction. The first half of the JE05 test cycle has relatively low exhaust gas temperatures, while the latter half has more high speed operation with rapidly increasing and higher catalyst temperature. Because of this, NOx trapped in the catalyst during the first half was desorbed and expelled during the high temperature second half, resulting in a lower NOx conversion rate for the entire test cycle.

Since a NOx trap catalyst cyclically releases and reduces NOx with rich exhaust gas, generating of a rich spike becomes important for application to diesel engines, which always operate with overall lean combustion. In addition, a NOx trap catalyst is poisoned and degraded in performance by the presence of SO2 in the exhaust gas. When the NOx absorbing efficiency thus decreases, it is necessary to regenerate the catalyst by a sulfur purge (desulfation) process in order to remove SO2. It is apparent that there are many factors and effects to understand before one can apply this catalyst system to a diesel engine, therefore we have carried out an inquiry into a performance of the NOx catalyst used the model gas equipment with known gas mixtures. The rich spike was generated with diesel fuel (light oil), resulting in a transient equivalence ratio spike > 1, to simulate diesel exhaust gas.

Diesel Particulate Filters (DPFs) having an effectiveness of around 90% reduction of particulate matter (PM) are an essential after-treatment technique in order to meet upcoming PM regulations (Japan2005, Euro4, US07), which are all increasingly stringent. The continuous-regenerating DPF system [1] has been drawing particular attention, because it is possible to significantly simplify the system and reduce costs. The study presented herein investigated the application of a continuous-regenerating DPF system to commercial vehicles. Since exhaust temperatures that are encountered during a significant portion of engine operation are too low to initiate oxidation of PM, a continuously regenerating DPF must employ an oxidation catalyst. However, when the basic characteristics were investigated, an adequate PM oxidation rate was not obtained during city mode operation, during which the exhaust temperature was notably low.

Although diesel engines have high thermal efficiency and excellent reliability, legislation in locations worldwide are calling for further reductions in nitrogen oxide (NOx) and particulate matter (PM). One possible method of compliance is a urea-SCR catalyst system to reduce NOx. It is widely known, and has been demonstrated in stationary engines, that there is a significant NOx reduction effect when a sufficient catalyst activation temperature is obtained. Recently several commercial vehicles have been outfitted a urea-SCR system to and characterized their NOx reduction effects. This report outlines the basic characteristics of the urea-SCR system, and evaluation of the effectiveness when used for heavy-duty diesel powered commercial vehicles. First, in order to investigate the basic characteristics of the urea-SCR catalyst, NOx reduction characteristics were measured using model gas equipment.

The purpose of this study is to explain the characteristics of homogeneous charge compression ignition. n-Heptane, which has the same cetane number as diesel fuel, was chosen for the fuel. A rapid compression machine was used to clarify the effects of air-fuel ratio, O2 concentration, and compression temperature on ignition delay and NOx emission. These investigations allowed the introduction of a formula for ignition delay.

A premixed compression-ignited (PCI) combustion system, which realizes lean combustion with high efficiency and low emissions, was investigated and its effects and problems were ascertained. With PCI combustion, fuel was injected early on the compression stroke and a premixed lean mixture was formed over a long mixing period. The test engine was operated with self-ignition of this premixed lean mixture. From the results of combustion observation and numerical simulation, a need to prevent the fuel spray from adhering to the cylinder liner and combustion-chamber wall was identified. Consequently, an impinged-spray nozzle with low penetration was made and tested. As a result, an extremely low nitrogen-oxide (NOx) emission level was realized but fuel efficiency was detracted slightly. Also, the engine operating range possible with PCI combustion was found to be limited to partial-load conditions and PCI combustion was found to cause an increase in hydrocarbon (HC) emission.

There is a gradient of fuel concentration in the conventional direct injection diesel engine fuel spray. Therefore, a region of stoichiometric mixture ratio exists in the spray and this results in production of large amounts of NOx. In this study, the fuel injection timing was advanced greatly to promote fuel and air mixing. Using this injection method, the engine could be operated with PREmixed lean DIesel Combustion (PREDIC), and NOx emissions were reduced greatly. To avoid collision of the fuel spray with the cylinder liner. the fuel was injected simultaneously with two side injectors. The two side injector sprays collided with each other and remained in the center region of the cylinder. Thus, mixing of the fuel and air was promoted by a long ignition delay period. Using conventional injection methods, NOx could not be reduced below 400ppm at an excess air ratio of 2.7. On the contrary. in the case of PREDIC, NOx emissions could be reduced to 20ppm at the same excess air ratio.

A conventional single cylinder direct injection diesel engine was fitted with three fuel injectors: one mounted vertically on the center, and the others mounted diagonally from the side direction. With this system, it was possible to control the fuel injection timing and injection quantity of each injector independently. It was also possible to independently control the fuel injection pressure of the center and side injectors. Using this system, it was possible to control the spatial and temporal distributions of the fuel injected into the combustion chamber, which are impossible to obtain with conventional injection equipment. In this study, an improvement in particulates and specific fuel consumption was obtained, while maintaining low NOx, by injecting a small amount of fuel from the two side injectors after the main fuel injection from the center injector.

The effects of a multi-hole nozzle with throttle construction (NTC) on combustion and emissions were investigated at high pressure fuel injection conditions. The throttle area was larger than the total injector hole area, therefore its fuel flow quantity was about the same as the standard nozzle under steady flow conditions. But the initial fuel injection rate was lower under unsteady flow conditions and smoke emissions were improved with the NTC. It is postulated that these effects were due to fuel flow turbulence inside the nozzle during the time of needle valve lift.

This paper presents the results of engine experiments and spray observations on a VCO nozzle. Two types of VCO nozzles having different hole shapes were investigated. One had a straight step hole (the VCO-S) and the other had a tapered step hole (the VCO-T). Both VCO nozzles could greatly reduce HC emissions in comparison to a standard nozzle. The VCO-S nozzle could reduce NOx emissions more than the VCO-T nozzle, and its spray penetration was shorter than that of the VCO-T.

To reduce exhaust emissions and fuel consumption, the effect of high pressure fuel injection was investigated with in-cylinder fuel spray observation and single cylinder engines. Spray impingement on the cavity wall promotes mixing with air and reduction in the nozzle area extends this wall impingement as a result of increasing both fuel injection pressure and injection period. There exists an optimum range for the injection period. Increased injection pressure by modifying injection rate of fuel pump and nozzle area, improves smoke and fuel consumption at low and medium speeds in particular. To extend these effects of high pressure injection, more optimized combustion system and minimized injection equipment drive torque must be required. To resolve the problem of high pressure injection such as higher combustion noise and increase in NOx emissions, the combination with pilot injection must be one of the most effective ways.