This study investigated the exhaust particle and unregulated emissions emanating from a heavy duty six-cylinder natural gas engine with CNG and HCNG fuels. Experiments were performed at different speeds (1000, 1500, 2000 and 2500 rpm) and load conditions (30%, 50%, 75% and 100%). Exhaust gas samples at each speed-load combination were analyzed for particle number concentration and particle size distribution using engine exhaust particle sizing spectrometer.
Unregulated emissions were also measured using FTIR (Fourier Transform Infrared) analyzer.
The results indicated that particle number (PN) concentration in exhaust is comparatively lower with HCNG fuel than CNG and it increases with increase in engine speed-load. At higher speed-load condition, engine emits high nucleation mode particles (NMP) and ultrafine particles (UFP). Total PN concentration in the NMP range is comparatively higher than UFP and accumulated mode particles (AMP) for both the test fuels. The surface area of particles corresponds to UFP and NMP are lower for HCNG at all test conditions.
The results on unregulated emission shows that major carboxyl (formaldehyde and acetaldehyde), alkane (propane and methane) and alkene (1,3-butadiene and propene) emissions were higher with CNG fuel than HCNG fuel. All these emissions decrease with increase in speed-load condition. Nitrogen oxides like NO2, NO and N2O shows comparatively higher value for HCNG due to proper and complete combustion. Average CO2 emission reduction in HCNG fuel is up to 17% as compared to CNG fuel. As load and speed increases, CO2 emission also increases for both the test fuels. Overall, this study exhibits the benefits of blending hydrogen in CNG in terms of reduction in particulate emission and unregulated emission.