Här lite mera att läsa (mina understryckningar)
BiogasMax
Exhaust gas aftertreatment and emissions of natural gas and biomethane driven vehicles
http://www.biogasmax.eu/media/d5_9_biog ... 012011.pdfsid 25
Citat:
HC emissions of NGVs almost entirely consist of methane
POTENTIAL OF NATURAL GAS POWERED VEHICLES IN
REDUCING CO2 AND POLLUTANT EMISSIONS UNDER REAL-
WORLD DRIVING CONDITIONS
http://www.fisita2010.com/programme/pro ... 10A035.pdf sid 1
Citat:
The results obtained show an acceptable pollutant emission performance of the considered
NGVs, having only 2 vehicles failing statutory hydrocarbon (HC) emission limit compliance.
But emissions of HC and nitrogen oxides (NOx) are remarkable in real-world urban hot
driving, indicating that the reduction of NOx in the catalytic converter employing HC as the
oxidant may not occur entirely because HC emissions of NGVs mainly consist of methane, a
powerful greenhouse gas that has a less pronounced catalytic oxidation activity. Besides,
pronounced emissions of HC and also ammonia together with low emissions of NOx in high
load and dynamic real-world rural and motorway driving indicate occasional fuel-rich
combustion. The often low-end engine control systems used for NGVs until now and the fact
that lambda sensors are cross-sensitive to methane are assumed to be responsible for this
observation. In contrast, neither cold start nor hot emissions of carbon monoxide (CO) and
non-methane hydrocarbons (NMHC) are critical.
http://www.unescap.org/ttdw/Publication ... lltext.pdfUN
ECONOMIC AND SOCIAL COMMISSION FOR ASIA AND THE PACIFIC
GUIDELINES FOR CONVERSION
OF DIESEL BUSES
TO COMPRESSED NATURAL GAS
sid 10 handlar om en VW Golf Bi-Fuel
Citat:
Advantages of CNG:
- 20 to 25 per cent less carbon dioxide;
- Up to 90 per cent less carbon monoxide;
- 75 to 90 per cent less non-methane hydrocarbons;
- Approximately 80 per cent less ozone-generating potential;
- No acrid smell from exhaust gases;
- No heavy metal additives necessary to increase knock rating;
- No losses through vaporization from the tank and/or while refuelling;
- No carcinogenic substances;
- No transport by road because natural gas is normally supplied via
pipelines.
Disadvantages of CNG
- Methane emission;
- Approximately 50 to 100 per cent more nitrogen oxides in comparison
with gasoline (with regulated 3-way catalytic converter);
- 10 to 20 per cent less power output with existing engines (which have
been optimized for gasoline and not for CNG operation);
- Additional fuel station network necessary;
- Weight and space requirements for gas cylinders in a vehicle;
- Shorter operating range of vehicles.
In summary, combustion of natural gas in an engine leads to overall fewer toxic
substances. Carbon monoxide and non-methane hydrocarbons are reduced by up to
approximately 90 per cent compared with gasoline, even without a catalytic converter. The 3-way
catalytic converter designed for gasoline remains largely ineffective for the degradation of
nitrogen oxides and methane in natural gas operation due to the low carbon monoxide values.
Further improvements can be achieved by using engines and catalytic converters optimized for
natural gas.
Determination of the catalytic converter performance of bi-fuel vehicle
http://www.academicjournals.org/JPTAF/P ... %20pdf.pdf(Här framgår det i resultaten att katalysatorn knappt fungerar alls i vid CNG drift medan den fungerar som vanligt på bensin)
sid 130
Citat:
Conclusions
1- It is found that the reason behind the increase of total
hydrocarbon (THC) in compressed natural gas (CNG)
operated vehicle over that produced in gasoline operated
vehicle is due to the difficulty in oxidizing the unburned
hydrocarbons in the exhaust gases, where the oxidization
of hydrocarbons is one of the functions of the three–way
catalyzer. The exhaust hydrocarbons of a gas-operated
vehicle have a significantly different composition to those
of a gasoline-operated vehicle.
Detta gäller bensinbilar men visar lite vad som händer med katalysatorns möjlighet att omvandla metan när den åldras:
Methane emission from automobile equipped with three-way catalytic converter while driving
http://www.sciencedirect.com/science/ar ... 4204002075Citat:
Abstract
In this study, the hydrocarbon emission from a three-way catalytic converter with a gasoline engine was investigated experimentally. The results reveal that converters have lower catalytic oxidation activity for methane than the other hydrocarbons, and degradation of the catalyst with use results in a significant effect on methane emission. The maximum methane concentration in exhaust using a converter with 78,000 km use is about 100 ppm, which is 1.4 times that for a new converter. The light-off temperature of the catalytic converter for hydrocarbon oxidation also rises from 548 to 598 K with an increase in the operating age of catalytic converter from 0 to 78,000 km. The ratio of CH4 concentration to total hydrocarbon increases with increasing vehicle speed and methane emission from the fuel of regular grade is higher than that of the premium grade.
Euro IV och V tillåter max 0,1 g HC per km i körcyklarna, vilket motsvarar ca 7,2 g CO2eq/km extra (på 20 år enigt IPCC)
Eftersom metan (CH4) inte kontrolleras i besiktningen vet vi inte om katalysatorn i en beg gasbil fortfarande fungerar och att de 0,1 g klaras av är inte alls säkert, ovanstånde artiklar tyder på att de relativt snabbt försämras och metanutsläppen under verkliga drift förhållanden är betydligt högre.