Adjusting nitrogen oxide ratios in exhaust gas

Abstract

A method of adjusting a ratio of NO to NO2 in a flow of exhaust gas is disclosed. The method includes directing a first portion of the exhaust flow through at least one first channel, wherein the at least one first channel is a wall-flow channel, and directing a second portion of the exhaust flow through at least one second channel, wherein the at least one second channel is an open flow-through channel. The method further includes converting NO into NO2 at a first rate in the first portion of the exhaust flow as the first portion of the exhaust flow passes through the at least one first channel and converting NO into NO2 at a second rate in the second portion of the exhaust flow as the second portion of the exhaust flow passes through the at least one second channel, the second rate being slower than the first rate.

Description

TECHNICAL FIELD [0001]The present disclosure is directed to treating exhaust gas expelled by internal combustion engines and, more particularly, to a system and method for adjusting nitrogen oxide ratios in exhaust gas.BACKGROUND [0002]Internal combustion engines, including diesel engines, gasoline engines, gaseous fuel-powered engines, and other engines known in the art, exhaust a complex mixture of air pollutants. These air pollutants may include solid material, known as particulate matter or soot, and gaseous compounds, such as hydrocarbons and the oxides of nitrogen (NOX). Due to increased concern over environmental pollution, exhaust emission standards have become more stringent and the amount of particulate matter and NOX emitted from an engine may be regulated depending on the type of engine, size of engine, and / or class of engine.[0003]One method implemented by engine manufacturers for complying with the regulation of particulate matter exhausted to the environment has been ...

AI Technical Summary

Benefits of technology

The present patent is about a method and apparatus for adjusting the ratio of NO to NO2 in a flow of exhaust gas. The method involves directing a portion of the exhaust gas through a wall-flow channel and another portion through an open flow-through channel. The method also includes converting NO into NO2 at different rates in the two channels, and trapping particulate matter in the first channel while passively regenerating it in the second channel. The technical effect of this patent is to provide a way to adjust the NO to NO2 ratio in exhaust gas and to remove particulate matter from the exhaust gas.

Problems solved by technology

This condition may be difficult to achieve because exhaust gas typically contains a ratio of NO to NO2 of approximately 10:1 (i.e., 90-95% NO and 5-10% NO2), when it exits a combustion engine.

Even when such a CDPF is used to bring the ratio of NO to NO2 somewhat closer to 1:1 prior to SCR, the method may be ineffective and / or inefficient.

Moreover, a CDPF coated with such a catalyst may be unable to trap particulate matter and / or convert hydrocarbons, as desired before the SCR process.

Although the system of the '464 patent may bring the ratio of NO and NO2 somewhat closer to the desired ratio of 1:1, it may be insufficient for producing the particular composition of exhaust flow which is desired to be sent to the SCR catalyst.

Moreover, the system may result in inefficient engine operation.

Specifically, if both the platinum-coated chamber and palladium-coated chamber are flow-through-type monoliths, the system may be unable to trap enough particulate matter to meet emissions standards.

Moreover, if both the platinum-coated chamber and palladium-coated chamber are wall-flow-type particulate filters, soot may build up in the palladium-coated chamber, thereby causing back pressure in the exhaust system and inefficient operation of the combustion engine.

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