Method and apparatus for treating diesel exhaust gas to remove fine particulate matter

• US 5,203,166 A
• Filed: 02/22/1991
• Issued: 04/20/1993
• Est. Priority Date: 02/22/1991
• Status: Expired due to Term

• Current Assignee: ECS Holdings Limited, Engine Control Systems Ltd. (United States)
• Original Assignee: Engine Control Systems Ltd. (United States)
• Inventors: Miller, John W.
• Primary Examiner(s): Hart, Douglas
• Application Number:
  US07/658,874
• Time in Patent Office: 788 Days
• Field of Search: 60/274, 60/286, 60/295, 60/303, 60/291, 60/297, 60/288, 55/466, 55/DIG. 30
• US Class Current: 60/274
• CPC Class Codes: F01N 13/009 having two or more separate purifying devices arranged in series
• CPC Class Codes: F01N 13/011 having two or more purifying devices arranged in parallel
• CPC Class Codes: F01N 2250/02 filtering and catalytic conversion
• CPC Class Codes: F01N 2330/06 Ceramic, e.g. monoliths
• CPC Class Codes: F01N 3/021 by means of filters
• CPC Class Codes: F01N 3/027 using electric or magnetic heating means
• CPC Class Codes: F01N 3/2882 Catalytic reactors combined or associated with other devices, e.g. exhaust silencers or other exhaust purification devices combined with absorbents or adsorbents only F01N3/0814; combined with particulate filters F01N3/035
• CPC Class Codes: F02B 3/06 with compression ignition compression ignition engines using air or gas for blowing fuel into compressed air in cylinder F02B13/02
• CPC Class Codes: Y10S 55/30 Exhaust treatment

Abstract

An emission control system for reducing particulates from exhaust gases from a diesel engine includes dual catalyzed diesel particulate filters in joint communication with the exhaust stream and a pair of heater elements each associated with one of the filters, through which exhaust gas is transmitted and uniformly heated. According to predetermined alternating heating sequence, the exhaust gas stream through first one of the pair of filters and then through the other is heated. The differing pressure differentials across the filters, determined by the heating sequence, effectively shift the major portion of the flow of exhaust gas between the filters, so that over the alternating heating sequence the heat generated by the heating elements is sufficient to clean the filters, without the requirement for any auxiliary source of combustion air or any mechanical switching means.

Claims

1. A method for regenerating a first ceramic filter and a second ceramic filer both loaded with particulates from exhaust gases of a diesel engine, said filters being in joint communication with the exhaust from a diesel engine and each being provided at the intake end thereof with first and second switchable heaters, respectively, operable when turned on to uniformly heat a stream of exhaust gas passing therethrough to a temperature sufficient to sustain combustion of particulate on said filters, comprising the steps of:

(a) turning on said first heater for a selected period of time, such that a portion of the particulates held by said first ceramic filter is burned off during passage of heated exhaust gases therethrough and the flow rate of exhaust gases through said fist ceramic filter becomes substantially greater than the flow rate of exhaust gases through said second ceramic filter;

(b) turning off said first heater and turning on said second heater for a selected period of time, such that the initially lower flow of heated exhaust gas through said second filer regenerates it essentially completely and the flow rate of exhaust gases through said second filter becomes greater than through the partially regenerated first filter;

(c) turning off said second heater and turning on said first heater for a selected period of time, such that the initially lower flow of heated exhaust gas through the partially regenerated first filter regenerates it essentially completely; and

(d) turning off said first heater and turning on said second heater for a selected period of time to ensure complete regeneration of said second filter,

wherein the exhaust from the diesel engine is passed through a catalytic purifier before passing through said first and second heaters.

2. An emissions control system for a diesel engine, comprising:

(i) a pair of ceramic catalyzed diesel particulate filters each having an intake end and an outlet end;

(ii) a pair of switchable electric heaters, each comprising a ceramic honeycomb monolith having a length of resistive wire winding threaded through a regular pattern of holes drilled through said monolith and means for connecting said wire winding to an external power source, each of said heaters being mounted to the intake end of one of said filters and operable when turned on to uniformly heat a stream of exhaust gas passing therethrough to a temperature sufficient to sustain combustion of particulate on the filter to which it is mounted;

(iii) an intake manifold connecting the upstream ends of said heater to the exhaust of said diesel engine, so that said filters are in joint communication at their intake ends with the exhaust gases generated by the engine; and

(iv) electronic sequencing means operable to turn one of said heaters on for a predetermined period at the commencement of a regeneration cycle for a system and then to turn the heaters alternately on and off for predetermined periods of time until both said diesel particulate filters have been essentially completely purged of particulate by heated exhaust gas stream passing therethrough.

3. An emissions control system according to claim 2, wherein the number and configuration of said holes is such that heat is uniformly distributed across said monolith when said power source is connected and said heater is turned on.

4. An emissions control system according to claim 3, wherein the length and resistance of said wire winding is such as to develop about 0.3 kW of heating power.

5. An emissions control system according to claim 2, further comprising electronic backpressure alarm means for detecting an unduly high engine backpressure arising from particulate loading of said filters.