Trapped burned gas fraction control for opposed-piston engines with uniflow scavenging

Patent metadata

Field	Value
Publication number	US-9284884-B2
Application number	US-201313974883-A
Country	US
Kind code	B2
Filing date	Aug 23, 2013
Priority date	Jun 25, 2013
Publication date	Mar 15, 2016
Grant date	Mar 15, 2016

Abstract

A trapped burned gas fraction is controlled in a two-stroke cycle opposed-piston engine with uniflow scavenging by adjusting an external EGR setpoint in real time. The adjusted setpoint is used to control EGR flow in the engine's air handling system.

First claim

The invention claimed is:

1. A uniflow-scavenged opposed-piston engine equipped with an air handling system, comprising:
at least one cylinder with a bore, longitudinally-spaced exhaust and intake ports, and a pair of pistons disposed in opposition in the bore and operative to open and close the exhaust and intake ports during operation of the engine;
a charge air channel to provide charge air to at least one intake port;
an exhaust channel to receive exhaust gas from at least one exhaust port;
an exhaust gas recirculation (EGR) loop having a loop input coupled to the exhaust channel and a loop output coupled to the charge air channel; and,
a control mechanization operable to:
determine a value of a trapped air handling parameter based on elements of combustion trapped in the cylinder by the last port of the cylinder to close during a cycle of engine operation and adjust the value of the trapped air handling parameter in response to a rate of EGR flow in the EGR loop; and
adjust the rate of EGR flow in the EGR loop based on the adjusted value of the trapped air handling parameter.

2. The opposed-piston engine of claim 1 , in which the control mechanization is operable to adjust the rate of EGR flow by operating a valve in the EGR loop to increase or decrease exhaust gas flow through the EGR loop.

3. The opposed-piston engine of claim 2 , in which the trapped air handling parameter is trapped burned gas fraction and the control mechanization is operable to:
determine a desired trapped burned gas fraction value for a current engine operating state;
determine a % EGR ratio defined by

%
⁢

⁢
E
⁢

⁢
G
⁢

⁢
R

=

W
egr

W

air
+

⁢

W
egr

 in which W egr is a mass flow rate of EGR gas in the EGR loop and W air is a mass flow rate of air into the charge air channel;
determine an error value based upon a difference between a desired % EGR ratio and a measured % EGR ratio; and,
adjust EGR flow by operating the valve in the EGR loop in response to the error value.

4. The opposed-piston engine of claim 2 , in which the control mechanization is operable to correct the value of the trapped air handling parameter based upon a trapped temperature parameter.

5. The opposed-piston engine of claim 4 , in which the trapped air handling parameter is trapped burned gas fraction and the control mechanization is operable to:
determine a desired trapped burned gas fraction value for a current engine operating state;
determine a % EGR ratio defined by

%
⁢

⁢
E
⁢

⁢
G
⁢

⁢
R

=

W
egr

W

air
+

⁢

W
egr

 in which W egr is a mass flow rate of EGR gas in the EGR loop and W air is a mass flow rate of air into the charge air channel;
determine an error value based upon a difference between a desired % EGR ratio and a measured % EGR ratio; and,
adjust EGR flow by operating the valve in the EGR loop in response to the error value.

6. A method of operating an opposed-piston engine, comprising:
generating exhaust gas in at least one ported cylinder of the engine;
transporting exhaust gas from an exhaust port of the ported cylinder through an exhaust channel;
recirculating a portion of the exhaust gas from the exhaust channel;
pressurizing fresh air;
mixing recirculated exhaust gas with the pressurized fresh air to form charge air;
pressurizing the charge air;
providing the charge air to an intake port of the ported cylinder;
determining a value of a trapped air handling parameter based on elements of combustion trapped in the cylinder by the last port of the cylinder to close during a cycle of engine operation;
adjusting the value of the trapped air handling parameter in response to a rate of EGR flow in the EGR loop; and
adjusting the rate of EGR flow in the EGR loop based on the adjusted value of the trapped air handling parameter.

7. The method of claim 6 , in which adjusting the rate of EGR flow includes operating a valve in the EGR loop to increase or decrease exhaust gas flow through the EGR loop.

8. The method of claim 7 , in which the trapped air handling parameter is trapped burned gas fraction and determining a value includes:
determining a desired trapped burned gas fraction value for a current engine operating state;
determining a % EGR ratio defined by

%
⁢

⁢
E
⁢

⁢
G
⁢

⁢
R

=

W
egr

W

air
+

⁢

W
egr

 in which W egr is a mass flow rate of EGR gas in the EGR loop and W air is a mass flow rate of air into the charge air channel;
determining an error value based upon a difference between a desired % EGR ratio and a measured % EGR ratio; and,
adjusting EGR flow by operating the valve in the EGR loop in response to the error value.

9. The method of claim 7 , in which the control mechanization is operable to correct the value of the trapped air handling parameter based upon a trapped temperature parameter.

10. The method of claim 9 , in which the trapped air handling parameter is trapped burned gas fraction and determining a value includes:
determining a desired trapped burned gas fraction value for a current engine operating s

Assignees

• Achates Power Inc

Inventors

• Nagar Nishit
• Quimby Donovan M

Classifications

• F01B7/14

  acting on different main shafts · CPC title

• F02B39/04

  Mechanical drives; Variable-gear-ratio drives (non-mechanical pump drives having variable gear ratio F02B39/08) · CPC title

• F02D41/1458

  with determination means using an estimation · CPC title

• Y02T10/144

  Cross-Sectional Technologies · mapped topic

• F02D2200/0411

  Volumetric efficiency · CPC title