Method and apparatus for operating a compression ignition engine

1. Method for controlling operation of an internal combustion engine configured to combust fuel in a compression-ignition combustion mode, comprising:

monitoring oxygen concentration in an exhaust gas feedstream of the internal combustion engine, mass flowrate of intake air, and a commanded fuel pulse of the fuel;

determining a stoichiometric air/fuel ratio of the fuel based on the oxygen concentration in the exhaust gas feedstream, the mass flowrate of intake air, and the commanded fuel pulse;

determining a first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel correlated to the stoichiometric air/fuel ratio of the fuel; and

controlling engine operation in response to the first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel;

wherein determining the stoichiometric air/fuel ratio of the fuel based on the oxygen concentration in the exhaust gas feedstream, the mass flowrate of intake air, and the commanded fuel pulse comprises determining the stoichiometric air/fuel ratio in accordance with the following relationship:

F

x

=

1

+

AFR

s

1

+

W

c

/

W

f

wherein

F x is an exhaust gas mass burned fraction determined based on the oxygen concentration in the exhaust gas feedstream,

AFR S is the stoichiometric air/fuel ratio of the engine fuel,

W c is a mass of fresh air flow into an intake manifold of the engine determined based on the mass flowrate of intake air, and

W f is an injected fuel mass determined based on the commanded fuel pulse.

2. The method of claim 1 , wherein controlling engine operation in response to the first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel comprises controlling a commanded EGR flowrate in response to the first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel.

3. The method of claim 1 , wherein controlling engine operation in response to the first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel comprises controlling a commanded fresh air flowrate in response to the first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel.

4. The method of claim 1 , wherein controlling engine operation in response to the first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel comprises controlling a commanded boost pressure in response to the first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel.

5. Method for controlling operation of an internal combustion engine configured to combust fuel in a compression-ignition combustion mode, comprising:

monitoring oxygen concentration in an exhaust gas feedstream of the internal combustion engine, mass flowrate of intake air, and a commanded fuel pulse of the fuel;

determining a stoichiometric air/fuel ratio of the fuel based on the oxygen concentration in the exhaust gas feedstream, the mass flowrate of intake air, and the commanded fuel pulse;

determining a first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel correlated to the stoichiometric air/fuel ratio of the fuel;

monitoring in-cylinder pressure;

determining a heating value of the fuel based on the in-cylinder pressure and the commanded fuel pulse;

determining a second blend ratio of biodiesel fuel and petrodiesel fuel of the fuel correlated to the heating value of the fuel; and

controlling engine operation in response to the first blend ratio of biodiesel fuel and petrodiesel fuel of the fuel and in response to the second blend ratio of biodiesel fuel and petrodiesel fuel of the fuel.

6. The method of claim 5 , wherein controlling engine operation in response to the first and second blend ratios of biodiesel fuel and petrodiesel fuel of the fuel comprises controlling a commanded EGR flowrate in response to the first and the second blend ratios of biodiesel fuel and petrodiesel fuel of the fuel.

7. The method of claim 5 , wherein controlling engine operation in response to the first and second blend ratios of biodiesel fuel and petrodiesel fuel of the fuel comprises controlling a commanded fresh air flowrate in response to the first and the second blend ratios of biodiesel fuel and petrodiesel fuel of the fuel.

8. The method of claim 5 , wherein controlling engine operation in response to the first and second blend ratios of biodiesel fuel and petrodiesel fuel of the fuel comprises controlling a commanded boost pressure in response to the first and the second blend ratios of biodiesel fuel and petrodiesel fuel of the fuel.

9. The method of claim 5 , wherein determining the heating value of the fuel based upon the in-cylinder pressure and the commanded fuel pulse comprises determining the heating value of the fuel corresponding to the in-cylinder pressure and the commanded fuel pulse in accordance with the following relationship:

z net ∝Q LHV *u *(δ fuel *g inj )

wherein

z net is the in-cylinder pressure,

Q LHV is the heating value of the fuel used in the commanded fuel pulse,

u is the commanded fuel pulse,

δ fuel is fuel density, and

g inj is injector scaling.

10. Method for controlling operation of an internal combustion engine configured to operate in a compression-ignition combustion mode, comprising:

monitoring in-cylinder pressure;

determining a heating value of the fuel based on the in-cylinder pressure and a commanded fuel pulse in accordance with the following relationship:

z net ∝Q LHV *u *(δ fuel *g inj )

wherein

z net is the in-cylinder pressure,

Q LHV is the heating value of the fuel used in the commanded fuel pulse,

u is the commanded fuel pulse,

δ fuel is fuel density, and

g inj is injector scaling;

determining a blend ratio of biodiesel fuel and petrodiesel fuel of the fuel correlated to the heating value of the fuel; and

controlling engine operation in response to the blend ratio of biodiesel fuel and petrodiesel fuel of the fuel.

11. The method of claim 10 , wherein controlling engine operation in response to the blend ratio of biodiesel fuel and petrodiesel fuel of the fuel comprises controlling a commanded EGR flowrate in response to the blend ratio of biodiesel fuel and petrodiesel fuel of the fuel.

12. The method of claim 10 , wherein controlling engine operation in response to the blend ratio of biodiesel fuel and petrodiesel fuel of the fuel comprises controlling a commanded fresh air flowrate in response to the blend ratio of biodiesel fuel and petrodiesel fuel of the fuel.

13. The method of claim 10 , wherein controlling engine operation in response to the blend ratio of biodiesel fuel and petrodiesel fuel of the fuel comprises controlling a commanded boost pressure in response to the blend ratio of biodiesel fuel and petrodiesel fuel of the fuel.

14. Method for operating an internal combustion engine configured to combust fuel in a compression-ignition combustion mode, comprising:

determining a heating value of fuel based on in-cylinder pressure and commanded engine fueling;

determining a stoichiometric air/fuel ratio of the fuel based on an oxygen concentration in the exhaust gas feedstream, a mass flowrate of intake air, and the commanded engine fueling;

determining a first blend ratio of biodiesel fuel and petrodiesel fuel correlated to the stoichiometric air/fuel ratio of the fuel;

determining a second blend ratio of biodiesel fuel and petrodiesel fuel correlated to the heating value of the fuel; and

controlling engine operation in response to the first and second blend ratios of biodiesel fuel and petrodiesel fuel.

15. The method of claim 14 , wherein monitoring in-cylinder pressure comprises monitoring in-cylinder combustion pressure during compression and expansion strokes of an engine cycle.

16. The method of claim 15 , wherein determining the heating value of the fuel based upon the in-cylinder pressure and the commanded fuel pulse comprises determining the heating value of the fuel corresponding to the in-cylinder pressure and the commanded fuel pulse in accordance with the following relationship:

z net ∝Q LHV *u *(δ fuel *g inj )

wherein

z net is the in-cylinder pressure,

Q LHV is the heating value of the fuel used in the commanded fuel pulse,

u is the commanded fuel pulse,

δ fuel is fuel density, and

g inj is injector scaling.

17. The method of claim 16 , wherein determining the stoichiometric air/fuel ratio of the fuel based on the oxygen concentration in the exhaust gas feedstream, the mass flowrate of intake air, and the commanded fuel pulse comprises determining the stoichiometric air/fuel ratio in accordance with the following relationship:

F

x

=

1

+

AFR

s

1

+

W

c

/

W

f

wherein

F x is an exhaust gas mass burned fraction determined based on the oxygen concentration in the exhaust gas feedstream,

AFR S is the stoichiometric air/fuel ratio of the engine fuel,

W c is a mass of fresh air flow into an intake manifold of the engine determined based on the mass flowrate of intake air, and

W f is an injected fuel mass determined based on the commanded fuel pulse.

18. The method of claim 14 , wherein determining the stoichiometric air/fuel ratio of the fuel based on the oxygen concentration in the exhaust gas feedstream, the mass flowrate of intake air, and the commanded fuel pulse comprises determining the stoichiometric air/fuel ratio in accordance with the following relationship:

F

x

=

1

+

AFR

s

1

+

W

c

/

W

f

wherein

F x is an exhaust gas mass burned fraction determined based on the oxygen concentration in the exhaust gas feedstream,

AFR S is the stoichiometric air/fuel ratio of the engine fuel,

W c is a mass of fresh air flow into an intake manifold of the engine determined based on the mass flowrate of intake air, and

W f is an injected fuel mass determined based on the commanded fuel pulse.