CLIAMS:I Claim:
1 A method of reducing smoke emission in a diesel engine, the method comprising:
retrieving a lambda value that corresponds to an engine operating condition;
characterized in said method
altering said lambda value such that altered lambda value maintains smoke emission within a smoke limit value and Nox emission within a Nox limit value;
calculating fresh air mass based on altered lambda value; and
determining percentage opening of an exhaust gas re-circulation (EGR) valve based on calculated fresh air mass.

2 The method as claimed in claim 1, wherein said retrieved lambda value is stored in a look up table in an electronic control unit.

3 The method as claimed in claim 1, wherein said percentage opening of said EGR valve is stored in look-up table in an electronic control unit.

4 An electronic control unit adapted to reduce smoke emission in a diesel engine, said electronic control unit operable to:
retrieve a lambda value that corresponds to an engine operating condition;
characterized in that
alter said lambda value for said engine operating condition such that altered lambda value maintains smoke emission within a smoke limit value and Nox emission within a Nox limit value;
calculate fresh air mass based on altered lambda value; and
determine percentage opening of an exhaust gas re-circulation (EGR) valve based on calculated fresh air mass.
,TagSPECI:Field of the invention
This invention relates to a method of reducing smoke emission in a diesel engine.

Background of the invention
During transient cycle, smoke emissions are predominant when vehicle is accelerated. To address this problem, the fuel quantity injected into the engine is reduced for a particular engine operating condition. When the fuel quantity is reduced, air/fuel ratio existing at that engine operating condition is sufficient to burn the reduced fuel quantity completely and thereby inhibiting increased smoke emission. An US patent number 4,428,354 discloses a technique to prevent undesirable smoke emissions by reducing injected fuel quantity. However, reduction of the fuel quantity causes undesirable drivability.

Another way to control smoke emission includes reducing the quantity of the exhaust gas re-circulated into the engine. However, this results in increased Nox emissions at certain engine operating conditions. Hence, there is still a need for a technique to maintain both smoke emissions and Nox emission within allowable limits to meet emission norms.

Brief description of the accompanying drawings

Figure 1 illustrates a block diagram representing a method of controlling exhaust gas flow rate in an exhaust gas recirculation (EGR) system.

Detailed description

Figure 1 illustrates a block diagram representing a method of reducing smoke emission in a diesel engine. In accordance with this disclosure, the method includes the following steps: retrieving a lambda value that corresponds to an engine operating condition represented as step 105. The method is further characterized by altering the lambda value such that altered lambda value maintains smoke emission within a smoke limit value and Nox emission within a Nox limit value represented as step 110, calculating fresh air mass based on altered lambda value represented as step 115, and determining a percentage opening of an exhaust gas re-circulation (EGR) valve based on calculated fresh air mass represented as step 120.

An electronic control unit is adapted to perform a method of reducing smoke emission in an internal combustion engine. The electronic control unit is configured to retrieve a lambda value for a particular engine operating condition. The lambda value may be retrieved from a look-up table, in the electronic control unit, that comprises a plurality of lambda values associated with a plurality of engine operating conditions.

The electronic control unit is also configured to alter the lambda value. The altered lambda value is such that it maintains smoke emission within a smoke limit value and Nox emission within a Nox limit value. In one case, for a particular engine operating condition, alteration of the lambda value may involve increase in the lambda value corresponding to that particular engine operating condition. In another case, alteration of the lambda value may involve decrease in the lambda value corresponding to that particular engine operating condition. Similarly, the lambda value associated with each engine operating conditions is altered. Such altered lambda values for various engine operating conditions are stored in a look-up table.

Upon altering the lambda value, the electronic control unit is configured to calculate fresh air mass based on the altered lambda value for that particular engine operating condition. The fresh air mass may be calculated using the following equation:

Lambda=((Fresh air mass)/(Fuel quantity))/14.5

where, Lambda is the altered lambda value
Fuel quantity is the quantity of fuel that is supplied for that particular engine operating condition.

The fuel quantity that is required to be supplied for that particular engine operating condition is stored in a look-up table in the electronic control unit. It should be noted that the fuel quantity corresponding to a particular engine operating condition is unaltered during the calculation of the fresh air mass.

The fresh air mass calculated, based on the altered lambda value, is greater than the actual fresh air mass for that particular engine operating condition that may be stored in a look-up table in the electronic control unit. Such increase in the fresh air mass due to altered lambda value enables complete combustion of the fuel, thereby reducing smoke emission.

The fresh air mass is calculated for a plurality of engine operating conditions based on corresponding altered lambda values. Also, it should be noted that various other means or equations can also be used to determine the fresh air mass. Further, the fresh air mass calculated for a plurality of engine operating conditions is stored in a look-up table in the electronic control unit.

The electronic control unit is further configured to determine a percentage opening of an EGR valve based on calculated fresh air mass. The percentage opening of the EGR valve is usually reduced because the increased quantity of fresh air replaces the exhaust gas. The percentage opening of the EGR valve that is determined, based on calculated fresh air mass, may be stored in a look-up table in the electronic control unit. The percentage opening of the EGR valve is determined, similarly, for a plurality of engine operating conditions and stored in the look-up table in the electronic control unit.

By increasing the supply of fresh air mass and reducing amount of the re-circulated exhaust gas, smoke emission, during transient cycle, is maintained within smoke limit value and simultaneously Nox emission is also maintained within Nox limit value. Also since the quantity of fuel that is required to be supplied is unaltered, better drivability is achieved.

It must be understood that the embodiments explained above are only illustrative and do not limit the scope of the disclosure. Many modifications in the embodiments with regard to alteration of the lambda value, calculation of the fresh air mass are envisaged and form a part of this invention. The scope of the invention is only limited by the claims.