Investigations of the Effect of Humid Air on NOₓ & PM Emissions of a CNG Engine

The objectives of the proposed investigation are to numerically and experimentally investigate the effect of a humid air system on nitrogen oxides (NOₓ) and Particulate Matter (PM) emissions of a compressed natural gas (CNG) engine. Experiments have shown that medium and heavy duty vehicles running on natural gas have lower PM, NOₓ, and non-methane hydrocarbon emissions, as compared to diesel and gasoline vehicles. However, recent U.S. Environmental Protection Agency/California Air Resources Board (EPA/CARB) regulations require much lower PM and NOₓ emissions from these vehicles. Humid air system or fumigation has been shown to be an effective approach in reducing NOₓ emissions of diesel engines. In this method, water vapor is injected into the intake air supplied for combustion. The process reduces the local temperature in the cylinders and raises the specific heat of the air-fuel mixture which also contributes to the elimination of the hot spots in the cylinders. With decreased temperature, NOₓ emissions are reduced. With an optimized system, the humid air system could substantially reduce NOₓ emissions without significant increase in hydrocarbon emissions. The proposed investigation is to investigate and quantify the effectiveness of the humid air system on emissions of a CNG engine.


  • English


  • Status: Completed
  • Funding: $89991
  • Contract Numbers:


  • Sponsor Organizations:

    California Department of Transportation

    1120 N Street
    Sacramento, CA  United States  95814

    Office of the Assistant Secretary for Research and Technology

    University Transportation Centers Program
    Department of Transportation
    Washington, DC  United States  20590
  • Project Managers:

    Nagra, Sukhdeep

  • Performing Organizations:

    National Center for Metropolitan Transportation Research

    University of Southern California
    650 Childs Way, RGL 107
    Los Angeles, CA  United States  90089-0626
  • Principal Investigators:

    Rahai, Hamid

  • Start Date: 20150815
  • Expected Completion Date: 20160814
  • Actual Completion Date: 20160814
  • Source Data: RiP Project 39741

Subject/Index Terms

Filing Info

  • Accession Number: 01572366
  • Record Type: Research project
  • Source Agency: National Center for Metropolitan Transportation Research
  • Contract Numbers: 65A0533
  • Created Date: Aug 6 2015 1:00AM