Method and system for estimating the specific gravity of an unknown fuel source in a multi-fuel engine

Patent metadata

Field	Value
Publication number	US-9546941-B2
Application number	US-201514703587-A
Country	US
Kind code	B2
Filing date	May 4, 2015
Priority date	May 4, 2015
Publication date	Jan 17, 2017
Grant date	Jan 17, 2017

Abstract

A method for estimating a specific gravity of a gaseous fuel is described. The gaseous fuel may power an engine and the engine may include a cylinder, a gas valve configured to supply an intake port of the cylinder with the gaseous fuel, a gas rail configured to deliver the gaseous fuel to the gas valve, and a microprocessor adapted to perform the method. The method may comprise establishing a pressure wave in the gas rail by opening and closing the gas valve, wherein the pressure wave travels at the speed of sound in the gaseous fuel. The method may further comprise determining a frequency of the pressure wave in the gas rail, and estimating the specific gravity of the gaseous fuel based on the frequency of the pressure wave.

First claim

What is claimed is:

1. A method for estimating a specific gravity of a gaseous fuel, the gaseous fuel powering an engine and the engine including a cylinder, a gas valve configured to supply an intake port of the cylinder with the gaseous fuel, a gas rail configured to deliver the gaseous fuel to the gas valve, and a microprocessor adapted to perform the method, said method comprising:
establishing a pressure wave in the gas rail by opening and closing the gas valve, the pressure wave traveling at a speed of sound in the gaseous fuel;
determining a frequency of the pressure wave in the gas rail; and
estimating the specific gravity of the gaseous fuel based on the frequency of the pressure wave.

2. The method of claim 1 , wherein estimating the specific gravity of the gaseous fuel based on the frequency of the pressure wave comprises:
determining the speed of sound in the gaseous fuel based on the frequency of the pressure wave;
estimating a specific gas constant for the gaseous fuel based on the speed of sound in the gaseous fuel;
estimating a molecular weight of the gaseous fuel based on the specific gas constant; and
estimating the specific gravity of the gaseous fuel based on the molecular weight of the gaseous fuel and a molecular weight of air.

3. The method of claim 1 , wherein estimating the specific gravity of the gaseous fuel based on the frequency of the pressure wave comprises comparing the frequency of the pressure wave with a calibration map that correlates gaseous fuel pressure wave frequencies with specific gravities.

4. The method of claim 1 , wherein estimating the specific gravity of the gaseous fuel based on the frequency of the pressure wave comprises:
determining the speed of sound in the gaseous fuel based on the frequency of the pressure wave;
calculating a molecular weight of the gaseous fuel based on the speed of sound in the gaseous fuel using a polynomial function relating speed of sound in gaseous fuels with gaseous fuel molecular weights; and
estimating the specific gravity of the gaseous fuel based on the molecular weight of the gaseous fuel and a molecular weight of air.

5. The method of claim 1 , wherein the engine is a multi-fuel engine and includes a plurality of cylinders, and wherein the method further comprises running one of the cylinders in gas mode in which the cylinder is supplied with the gaseous fuel as a primary fuel source prior to establishing the pressure wave in the gas rail.

6. The method of claim 5 , wherein the engine is a V-engine, and wherein running one of the cylinders in gas mode comprises running one cylinder in each bank in gas mode.

7. The method of claim 2 , wherein determining the specific gas constant for the gaseous fuel based on the speed of sound is performed by solving the equation c=sqrt(kR s T) for R s , where c is the speed of sound in the gaseous fuel, k is a specific heat ratio of the gaseous fuel, T is temperature, and R s is the specific gas constant of the gaseous fuel.

8. The method of claim 7 , wherein determining the molecular weight of the gaseous fuel based on the specific gas constant is performed using the equation MW G =R/R s , where MW G is the molecular weight of the gaseous fuel, R is the ideal gas constant, and R s is the specific gas constant for the gaseous fuel.

9. The method of claim 8 , wherein estimating the specific gravity of the gaseous fuel based on the molecular weight of the gaseous fuel and the molecular weight of air is performed using the equation SG Ge =MW G /MW air , where SG Ge is the specific gravity of the gaseous fuel, MW G is the molecular weight of the gaseous fuel, and MW air is the molecular weight of air.

10. An engine powered by a gaseous fuel having an unknown specific gravity, comprising:
at least one cylinder having a combustion chamber disposed therein;
a piston positioned for displacement within the cylinder;
an intake port configured to deliver a mixture of air and the gaseous fuel to the cylinder;
a gas valve configured to regulate a gas mass flow into the intake port;
a gas rail configured to supply the gas valve with the gaseous fuel, the gas valve being configured to generate a pressure wave in the gas rail when the gas valve is opened and closed;
a pressure sensor in the gas rail configured to detect the pressure wave; and
a specific gravity estimation module configured to determine a frequency of the pressure wave detected by the pressure sensor, and to estimate the specific gravity of the gaseous fuel based on the frequency of the pressure wave.

11. The engine of claim 10 , wherein the specific gravity estimation module further comprises:
a speed of sound module configured to determine a speed of sound in the gaseous fuel based on the frequency of the pressure wave;
a specific gas constant module configured to estimate a specific gas constant of the gaseous fuel based on the speed of sound in the gaseous fuel;
a molecular weight module configured to estimate a molecular weight of the gaseous fuel based on the specific gas constant of the gaseous fuel; and
a specific gravity module configured to estimate the specific gravity of the gaseous fuel based on the molecular weight of the gaseous fuel and a molecular weight of air.

12. The engine of claim 10 , wherein the specific gravity estimation module is configured to estimate the specific gravity of the gaseous fuel by comparing the frequency of the pressure wave with a calibration map that correlates gaseous fuel pressure wave frequencies with specific gravities.

13. The engine of claim 10 , wherein the specific gravity estimation module further comprises:
a speed of sound module configured to determine a speed of sound in the gaseous fuel based on the frequency of the pressure wave;
a molecular weight module configured to calculate a molecular weight of the gaseous fuel based on the speed of sound in the gaseous fuel using a polynomial function relating speed of sound in gaseous fuels with gaseous fuel molecular weights; and
a specific gravity module configured to estimate the specific gravity of the gaseous fuel based on the molecular weight of the gaseous fuel and a molecular weight of air.

14. The engine of claim 10 , wherein the engine is a multi-fuel engine having a plurality of cylinders, and wherein the specific gravity estimation module further includes a learning mode module configured to set one of the cylinders in gas mode in which the cylinder is supplied with the gaseous fuel as a primary fuel source.

15. The engine of claim 14 , wherein the engine is a V-engine, and wherein the learning mode module is configured to set one of the cylinders in each bank of the V-engine in gas mode.

16. The engine of claim 14 , wherein the engine is an in-line engine, and wherein the learning mode module is configured to run one of the cylinders in a row of cylinders in gas mode.

17. The engine of claim 11 , wherein the specific gas constant module is configured to determine the specific gas constant of the gaseous fuel by solving the equation c=sqrt(kR s T) for R s , where c is the speed of sound in the gaseous fuel, k is a specific heat ratio of the gaseous fuel, T is temperature, and R s is the specific gas constant for the gaseous fuel.

18. The engine of claim 17 , wherein the molecular weight determination module is configured to determine the molecular weight of the gaseous fuel using the equation MW G =R/R s , where MW G is the molecular weight of the gaseous fuel, R is the ideal gas constant, and R s is the specific gas constant for the gaseous fue

Assignees

• Caterpillar Inc

Inventors

• Rasmussen Jason
• Zook Brett
• Deng Baoyang
• Sivasubramanian Arvind

Classifications

• G01N9/36

  Analysing materials by measuring the density or specific gravity, e.g. determining quantity of moisture (methods of measurement in general G01N9/02 - G01N9/32) · CPC title

• F02D2200/0612

  determined by estimation · CPC title

• G01N9/26

  by measuring pressure differences · CPC title

• F02D2200/0611

  Fuel type, fuel composition or fuel quality · CPC title

• F02B43/10

  Engines or plants characterised by use of other specific gases, e.g. acetylene, oxyhydrogen · CPC title