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

Project Number


Project Summary

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. 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. 

Project Status




Topic Area

Integrated Freight and Passenger Systems

P.I. Name & Address

Professor, Department of Mechanical and Aerospace Engineering; College of Engineering
California State University Long Beach
1250 Bellflower Blvd.
Long Beach, CA 90840
United States

Funding Source


Total Project Cost


Agency ID or Contract Number

Grant No: 65A0533

Start and End Dates

8/15/2015 to 8/14/2016