Search Results

Mechanisms of NH₃ generation using LNT-like catalysts have been studied in a bench reactor over a wide range of temperatures, flow rates, reformer catalyst types and synthetic exhaust-gas compositions. The experiments showed that the on board production of sufficient quantities of ammonia on board for SCR operation appeared feasible, and the results identified the range of conditions for the efficient generation of ammonia. In addition, the effects of reformer catalysts using the water-gas-shift reaction as an in-situ source of the required hydrogen for the reactions are also illustrated. Computations of the NH₃ and NOx kinetics have also been carried out and are presented. Design and impregnation of the SCR catalyst in proximity to the ammonia source is the next logical step. A heated synthetic-exhaust gas flow bench was used for the experiments under carefully controlled simulated exhaust compositions.

In recent years, catalyst systems such as a lean NOx trap (LNT) catalyst system and a urea selective catalytic reduction (SCR) system have been developed to obtain cleaner diesel emissions. At Nissan, we developed an emission control system for meeting Tier 2 Bin 5 requirements in 2003. On the basis of that technology, a new HC-NOx trap catalyst system has now been developed that complies with the SULEV standards without increasing the catalyst volume and precious metal loading. Compliance with the SULEV standards requires a further reduction of HC (NMHC) emissions by 84% and NOx by 60% compared with the emission performance Tier 2 Bin 5 compliant catalyst system. Consequently high conversion performance for both HCs and NOx is needed. An investigation of HC emission behavior under the FTP75 mode showed that a reduction of cold-phase HCs was critical for meeting the standard. Large quantities of HCs above C4 are emitted in the cold state.

Hydrogen can be produced by electrolyzation with renewable electricity and the combustion products of hydrogen mixture include no CO, CO2 and hydrocarbons. In this study, engine performance with hydrogen / diesel dual fuel (hydrogen DDF) operation in a multi-cylinder diesel engine is investigated due to clarify advantages and disadvantages of hydrogen DDF operation. Hydrogen DDF operation under several brake power conditions are evaluated by changing a rate of hydrogen to total input energy (H2 rate). As H2 rate is increased, an amount of diesel fuel is decreased to keep a given torque constant. When the hydrogen DDF engine is operated with EGR, Exhaust gas components including carbon are improved or suppressed to same level as conventional diesel combustion. In addition, brake thermal efficiency is improved to 40% by increase in H2 rate that advances combustion phasing under higher power condition. On the other hand, NOx emission is much higher than one of conventional diesel engine.

It is generally known that NOx reacts with unburned gasoline, olefins in particular, to form sludge precursors. In this study, the authors investigated the process by which NOx and unburned gasoline mix into the engine oil and analyzed the mechanism whereby stop and go driving accelerates sludge formation. It has been found that NOx detected in the engine oil as nitrite ions mixes into the oil in the crankcase. The NOx concentration in the engine oil increases rapidly when the crankcase gas temperature is nearly equal to the dew point of the water vapor in the crankcase. Unburned gasoline is mainly absorbed into the oil through the oil film on the cylinder walls and the oil in the ring grooves. During low-temperature engine operation in stop-go driving (i.e., when the vehicle is stopped), NOx and unburned gasoline are absorbed into the engine oil and, in high-temperature engine operation (i.e., when the vehicle is moving), NOx and unburned gasoline are released from the oil.

Selective catalytic reduction (SCR) of nitrogen oxides (NOx) is used in diesel-fueled mobile applications where urea is an added reducing agent. We show that the Ultera® dual-stage catalyst, with intercooling aftertreatment system, intrinsically performs the function of the SCR method in nominally stoichiometric gasoline vehicle engines without the need for an added reductant. We present that NOx is reduced during the low-temperature operation of the dual-stage system, benefiting from the typically periodic transient operation (acceleration and decelerations) with the associated swing in the air/fuel ratio (AFR) inherent in mobile applications, as commonly expected and observed in real driving. The primary objective of the dual-stage aftertreatment system is to remove non-methane organic gases (NMOG) and carbon monoxide (CO) slip from the vehicle’s three-way catalyst (TWC) by oxidizing these constituents in the second stage catalyst.

Diesel emissions are significant issue worldwide, and emissions requirements have become so tough that. the application of after-treatment systems is now indispensable in many countries To meet even more stringent future emissions requirements, it has become apparent that the improvement of market fuel quality is essential as well as the development in engine and exhaust after-treatment technology. Japan Clean Air Program II (JCAP II) is being conducted to assess the direction of future technologies through the evaluation of current automobile and fuel technologies and consequently to realize near zero emissions and carbon dioxide (CO2) emission reduction. In this program, effects of fuel properties on the performance of diesel engines and a vehicle equipped with two types of diesel NOx emission after-treatment devices, a Urea-SCR system and a NOx storage reduction (NSR) catalyst system, were examined.

In Biodiesel Fuel Research Working Group(WG) of Japan Auto-Oil Program(JATOP), some impacts of high biodiesel blends have been investigated from the viewpoints of fuel properties, stability, emissions, exhaust aftertreatment systems, cold driveability, mixing in engine oils, durability/reliability and so on. In the impact on exhaust emissions, the impact of high biodiesel blends into diesel fuel on diesel emissions was evaluated. The wide variety of biodiesel blendstock, which included not only some kinds of fatty acid methyl esters(FAME) but also hydrofined biodiesel(HBD) and Fischer-Tropsch diesel fuel(FTD), were selected to evaluate. The main blend level evaluated was 5, 10 and 20% and the higher blend level over 20% was also evaluated in some tests. The main advanced technologies for exhaust aftertreatment systems were diesel particulate filter(DPF), Urea selective catalytic reduction (Urea-SCR) and the combination of DPF and NOx storage reduction catalyst(NSR).

It has been found that over Rh/a specified support NOx is eliminated using rich/lean excursions in a different reaction mechanism from a Lean NOx Trap system, where NO is decomposed into nitrogen and oxygen. The contribution of the transient NOx direct decomposition to NOx elimination depends on both reaction conditions and supports. 0.1-0.5wt%Rh and 0.5wt%Pd/a specified support: X can mainly catalyze the transient NO decomposition. On the other hand, on another Rh-based catalyst NO reduction proceeds mainly in the Lean NOx trap system. As expected from the NO elimination mechanism, the newly developed catalyst has shown a high tolerance against SOx.

Experimental investigations were conducted with a direct-injection diesel engine to improve exhaust emission, especially nitrogen oxide (NOx) and particulate matter (PM), without increasing fuel consumption. As a result of this work, a new combustion concept, called Modulated Kinetics (MK) combustion, has been developed that reduces NOx and smoke simultaneously through low-temperature combustion and premixed combustion, respectively. The characteristics of a new combustion concept were investigated using a single cylinder DI diesel engine and combustion photographs. The low compression ratio, EGR cooling and high injection pressure was applied with a multi-cylinder test engine to accomplish premixed combustion at high load region. Combustion chamber specifications have been optimized to avoid the increase of cold-start HC emissions due to a low compression ratio.

Experimental investigations were previously conducted with a direct-injection diesel engine with the aim of reducing exhaust emissions, especially nitrogen oxides (NOx) and particulate matter (PM). As a result of that work, a combustion concept, called Modulated Kinetics (MK) combustion, was developed that reduces NOx and smoke simultaneously through low-temperature combustion and premixed combustion to achieve a cleaner diesel engine. In subsequent work, it was found that applying a low compression ratio was effective in expanding the MK combustion region on the high-load side. The MK concept was then combined with an exhaust after-treatment system and applied to a test vehicle. The results indicated the attainment of ULEV emission levels, albeit in laboratory evaluations. In the present work, the combination of the MK combustion concept and certain fuel properties has been experimentally investigated with the aim of reducing exhaust emissions further.

Single cylinder engine testing was carried out to clearly understand the test results of multi-cylinder engines reported by the Diesel WG in JCAP (Japan Clean Air Program) (1), (2), (3) and (4). In this tests, engine specifications such as fuel injection pressure, nozzle hole diameter, turbo-charging pressure, EGR rate, and fuel properties such as 1-, 2-, 3-ring aromatics content, n-,i-paraffins content, and T90 were parametrically changed and their influence on the emissions were studied. PM emission generally increased in each engine condition with increased aromatic contents and T90. In particular, multi ring aromatics brought about large increases in PM regardless of the engine conditions. The influence of fuel properties on NOx emission is smaller than the influence on PM emission. Some other fuels that have various side chain structures of 1-ring aromatics, normal paraffins only and various naphthene contents were also investigated.

This paper describes the third generation of the partial zero emission vehicle (P-ZEV) technology originally adopted on the Nissan Sentra CA sold in California. The 2000 Nissan Sentra CA became the world's first gasoline-fueled car to qualify for P-ZEV credits from the California Air Resources Board (CARB). The third-generation P-ZEV system has been substantially reduced in size and cost, compared with the Sentra CA system, enabling it to be used on high-volume models. This system complies with the P-ZEV requirements, including those for zero evaporative emissions and Onboard Diagnostics II (OBD-II). To achieve a more compact and lower-cost system, an ultra-thin-walled catalyst substrate, the world's first to attain a 1.8-mil wall thickness, has been adopted along with catalysts that display excellent low-temperature activity. As a result, low-temperature catalyst activity has been significantly improved.

This paper describes the emission reduction technologies applied to 4- and 6-cylinder engines used on Japanese market models certified as ultra-low emission vehicles (U-LEVs) in Japan. To qualify for this rigorous U-LEV certification, a vehicle must reduce hydrocarbon (HC) and nitrogen oxide (NOx) emissions by an additional 75% from the levels mandated by Japan's 2000 exhaust emission regulations. Nearly all Nissan Japanese models fitted with a gasoline engine, ranging from in-line 4-cylinder engines to V6 engines, have now been certified as U-LEVs. This has been accomplished by further improving the emission reduction technologies that were developed for the Sentra CA, which was launched in the U.S. market in 2000 as the world's first gasoline-fueled vehicle to qualify for Partial Zero Emission Vehicle (P-ZEV) credits from the California Air Resources Board. The specific new technologies involved are as follows.

Urea/SCR systems have been proven effective at reducing NOx over a wide range of operating conditions on mid/heavy duty diesel vehicles. However, design changes due to reduction in the size of modern compact Urea/SCR systems and lower exhaust temperature have increased the possibility of urea deposit formation. Urea deposits are formed when urea in films and droplets undergoes undesirable secondary reactions and generate by-products such as ammelide, biuret and cyanuric Acid (CYA). Ammelide and CYA are difficult to decompose which lead to the formation of solid deposits on the surface. This phenomenon degrades the performance of the after treatment system by decreasing overall mixing efficiency, lowering de-NOx efficiency and increasing pressure drop. Therefore, mitigating urea deposits is a primary design goal of modern diesel after-treatment systems.

In the Japan Clean Air Program II (JCAP II) Diesel WG, effects of fuel properties on the performance of two types of diesel NOx emission aftertreatment devices, a Urea-SCR system and a NOx storage reduction (NSR) catalyst system, were examined. For a Urea-SCR system, the NOx emission reduction performance with and without an oxidation catalyst installed in front of the SCR catalyst at low exhaust gas temperature operation was compared. For an NSR catalyst system, the effect of fuel sulfur on both emissions and fuel economy during 50,000 km driving was examined. Furthermore, effects of other fuel properties such as distillation on exhaust emissions were investigated. The results show that sulfur is the influential factor for both devices. Namely, high NOx emission reduction performance of the Urea-SCR system with the oxidation catalyst at low exhaust gas temperature operation is influenced by sulfur.

Clarifying the impact of ETBE 8% blended fuel on current Japanese gasoline vehicles, under the Japan Clean Air Program II (JCAPII) we conducted exhaust emission tests, evaporative emission tests, durability tests on the exhaust after-treatment system, cold starting tests, and material immersion tests. ETBE 17% blended fuel was also investigated as a reference. The regulated exhaust emissions (CO, HC, and NOx) didn't increase with any increase of ETBE content in the fuel. In durability tests, no noticeable increase of exhaust emission after 40,000km was observed. In evaporative emissions tests, HSL (Hot Soak Loss) and DBL (Diurnal Breathing Loss) didn't increase. In cold starting tests, duration of cranking using ETBE 8% fuel was similar to that of ETBE 0%. In the material immersion tests, no influence of ETBE on these material properties was observed.

Emission regulations for diesel-powered vehicles have been gradually tightening. Installation of after-treatment devices such as diesel particulate filters (DPF), NOx storage reduction (NSR) catalysts, and so on is indispensable to satisfy rigorous limits of particulate matter (PM) and nitrogen oxides (NOx). Japan Clean Air Program II Oil Working Group (JCAPII Oil WG) has been investigating the effect of engine oil on advanced diesel after-treatment devices. First of all, we researched the impact of oil-derived ash on continuous regeneration-type diesel particulate filter (CR-DPF), and already reported that the less sulfated ash in oil gave rise to lower pressure drop across CR-DPF [1]. In this paper, impact of oil-derived sulfur and phosphorus on NSR catalyst was investigated using a 4L direct injection common-rail diesel engine with turbo-intercooler. This engine equipped with NSR catalyst meets the Japanese new short-term emission regulations.

Long-haul and other heavy-duty trucks, presently almost entirely powered by diesel fuel, face challenges meeting worldwide needs for greatly reducing nitrogen oxide (NOx) emissions. Dual-fuel gasoline-alcohol engines could potentially provide a means to cost-effectively meet this need at large scale in the relatively near term. They could also provide reductions in greenhouse gas emissions. These spark ignition (SI) flexible fuel engines can provide operation over a wide fuel range from mainly gasoline use to 100% alcohol use. The alcohol can be ethanol or methanol. Use of stoichiometric operation and a three-way catalytic converter can reduce NOx by around 90% relative to emissions from diesel engines with state of the art exhaust treatment.

An analysis was made of wear factors by investigating the effect of engine operating conditions on valve train wear. It was found that cam nose wear increased as larger amounts of combustion products, including nitrogen oxides and unburned gasoline, became intermixed with the engine oil. Based on these results, a valve train wear test procedure has been developed for evaluating cam nose and rocker arm wear under engine firing conditions. It has been confirmed that this test procedure correlates will with ASTM Sequence VE test and CCMC TU-3 test.

The effect of the introduction of low-emission vehicles on potential air quality improvement in the Los Angeles area was predicted using a three-dimensional airshed simulation model. The simulations were based on ozone concentration estimates made on the basis of data released by the California Air Resources Board concerning projected quantities of emissions from various sources in 2010. Analyses were made of three scenarios. One assumed that LEV, ULEV and ZEV regulations were enforced as planned, a second assumed that these planned regulations were modified; and a third assumed that emission levels from various sources were reduced in line with the goals of the Air Quality Management Plan formulated by the South Coast Air Quality Management District.