ISO 15403 - CNG Quality

ISO 15403 specifies requirements for natural gas used as compressed fuel for vehicles (CNG).

Table of Contents

Overview

Standard: ISO 15403-1:2006 - Natural gas — Natural gas for use as a compressed fuel for vehicles

Purpose: Assess natural gas quality for use in vehicle engines by calculating:

Class: Standard_ISO15403

Calculated Parameters

Motor Octane Number (MON)

MON indicates knock resistance. Calculated from gas composition:

\[MON = 137.78 \cdot x_{CH_4} + 29.948 \cdot x_{C_2H_6} - 18.193 \cdot x_{C_3H_8} - 167.062 \cdot (x_{nC_4} + x_{iC_4}) + 181.233 \cdot x_{CO_2} + 26.944 \cdot x_{N_2}\]

where $x_i$ is the mole fraction of component i.

Methane Number (MN)

MN is derived from MON:

\[MN = 1.445 \cdot MON - 103.42\]

Interpretation:

Implementation

Constructor

import neqsim.standards.gasquality.Standard_ISO15403;

// Create from gas composition
Standard_ISO15403 iso15403 = new Standard_ISO15403(thermoSystem);

Key Methods

Method Description
calculate() Calculate MON and MN
getValue("MON") Get Motor Octane Number
getValue("MN") Get Methane Number

Usage Examples

Basic Calculation

import neqsim.thermo.system.SystemSrkEos;
import neqsim.standards.gasquality.Standard_ISO15403;

// CNG composition
SystemInterface cng = new SystemSrkEos(273.15 + 15, 200.0);
cng.addComponent("methane", 0.92);
cng.addComponent("ethane", 0.04);
cng.addComponent("propane", 0.01);
cng.addComponent("n-butane", 0.002);
cng.addComponent("i-butane", 0.003);
cng.addComponent("CO2", 0.015);
cng.addComponent("nitrogen", 0.01);
cng.setMixingRule("classic");

// Calculate methane number
Standard_ISO15403 iso15403 = new Standard_ISO15403(cng);
iso15403.calculate();

double mon = iso15403.getValue("MON");
double mn = iso15403.getValue("MN");

System.out.printf("Motor Octane Number (MON) = %.1f%n", mon);
System.out.printf("Methane Number (MN) = %.1f%n", mn);

Effect of Composition on Methane Number

// Analyze MN sensitivity to C2+ content
double[] ethaneContents = {0.01, 0.03, 0.05, 0.08, 0.10};

System.out.println("Ethane (mol%) | MON   | MN");
System.out.println("--------------|-------|------");

for (double c2 : ethaneContents) {
    SystemInterface gas = new SystemSrkEos(273.15 + 15, 200.0);
    gas.addComponent("methane", 0.97 - c2);
    gas.addComponent("ethane", c2);
    gas.addComponent("CO2", 0.02);
    gas.addComponent("nitrogen", 0.01);
    gas.setMixingRule("classic");
    
    Standard_ISO15403 std = new Standard_ISO15403(gas);
    std.calculate();
    
    System.out.printf("%13.0f | %.1f | %.1f%n", 
        c2 * 100, 
        std.getValue("MON"), 
        std.getValue("MN"));
}

CO2 and N2 Effects

// CO2 and N2 improve methane number
SystemInterface leanGas = new SystemSrkEos(273.15 + 15, 200.0);
leanGas.addComponent("methane", 0.85);
leanGas.addComponent("ethane", 0.05);
leanGas.addComponent("propane", 0.02);

// Base case - no inerts
leanGas.addComponent("CO2", 0.0);
leanGas.addComponent("nitrogen", 0.0);
leanGas.setMixingRule("classic");

Standard_ISO15403 baseStd = new Standard_ISO15403(leanGas);
baseStd.calculate();
System.out.printf("Base case MN: %.1f%n", baseStd.getValue("MN"));

// With 5% CO2
SystemInterface withCO2 = leanGas.clone();
withCO2.addComponent("CO2", 0.05);
Standard_ISO15403 co2Std = new Standard_ISO15403(withCO2);
co2Std.calculate();
System.out.printf("With 5%% CO2 MN: %.1f%n", co2Std.getValue("MN"));

// With 5% N2
SystemInterface withN2 = leanGas.clone();
withN2.addComponent("nitrogen", 0.05);
Standard_ISO15403 n2Std = new Standard_ISO15403(withN2);
n2Std.calculate();
System.out.printf("With 5%% N2 MN: %.1f%n", n2Std.getValue("MN"));

Methane Number Concepts

Component Effects

Component Effect on MN
Methane Increases MN
Ethane Slight decrease
Propane Moderate decrease
Butanes Strong decrease
CO₂ Increases MN
N₂ Increases MN
H₂ Decreases MN

Typical Values

Gas Type Typical MN
Pure methane 100
Lean natural gas 85-95
Associated gas 70-85
Biogas 130-140
LNG regasified 75-90

Specifications

Region Minimum MN
Europe (typical) 65-70
Germany (DIN 51624) 70
California 80

Technical Notes

Correlation Validity

The correlation is valid for:

Limitations

  1. Does not account for C5+ hydrocarbons
  2. Hydrogen effects not included in correlation
  3. Best for pipeline-quality natural gas

Alternative Methods

For more complex gases, consider:

References

  1. ISO 15403-1:2006 - Natural gas — Natural gas for use as a compressed fuel for vehicles — Part 1: Designation of the quality
  2. DIN 51624 - Automotive fuels - Compressed natural gas - Requirements and test methods
  3. SAE J1616 - Recommended Practice for Compressed Natural Gas Vehicle Fuel