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With alternative fuels having moved more into market in light of their reduction of emissions of CO2 and other air pollutants, the spark ignited internal combustion engine design has only been affected to small extent. The development of combustion engines running on natural gas or Biogas have been focused to maintain driveability on gasoline, creating a multi fuel platform which does not fully utilise the alternative fuels’ potential. However, optimising these concepts on a fundamental level for gas operation shows a great potential to increase the level of utilisation and effectiveness of the engine and thereby meeting the emissions legislation. The project described in this paper has focused on optimising a combustion concept for CNG combustion on a single cylinder research engine. The ICE’s efficiency at full load and the fuels characteristics, including its knock resistance, is of primary interest - together with part load performance and overall fuel consumption.

The present wording on implementing regulation on type-approval of motor vehicles and engines with respect to emissions from heavy-duty vehicles in Europe (e.g., Euro VI requirements) describes the procedure to determine gaseous emissions from on-road measurements using Portable Emissions Measurement Systems (PEMS). The gaseous emissions to be measured according to the PEMS protocol includes carbon monoxide (CO), total hydrocarbons (THC) and nitrogen oxides (NOx) for diesel engines and with the addition of methane (CH₄) for gas engines. Measurement methods of particles are at this stage under development. Emission data from on-road testing can be used for calculation of In-service Conformity (IsC) pass/fail criteria but also for establishing local emission factors for specific routes. The procedure for the measurement is described in detail in the regulation.

The present wording of implementing the regulation for type-approval of motor vehicles and engines with respect to emissions from heavy-duty vehicles (e.g., Euro VI requirements) describes the procedure to determine gaseous emissions from on-road measurements using Portable Emissions Measurement Systems (PEMS). Emissions to be measured according to the PEMS protocol are carbon monoxide (CO), total hydrocarbons (HC) nitrogen oxides (NOx) and carbon dioxide (CO₂). Measurement methods of particles will be included in the Euro VI requirements. Emission results from on-road testing can be used for In Service Conformity (ISC) pass/fail criteria but also for establishing emission factors for specific routes and verification of the fuel impact on the emissions.

In the EU regulations, specification's for diesel fuel quality is regulated in the standard EN590. Sweden has however for many years used an “Environmental Class 1” (EC1) diesel fuel. In addition to fulfilling the EN590 standard, the main difference today between the Swedish EC1 and the EN590 fuel specifications is that higher levels of aromatics and polyaromatics (PAH) are allowed in the EN590 standard. Aromatics are considered to be potentially mutagenic, and the higher levels of aromatics also lead to increased particle emissions. Earlier studies of the exhaust emissions from engines using the different fuel qualities have shown significant differences, both regarding regulated emissions and health effects. In these studies, vehicles from emission standard Euro III and older have been used. The scope of this study was to investigate whether the differences persist for a modern Euro V vehicle or not.

Alternative-fuelled vehicles are a growing market, and emission performance of these vehicles should be thoroughly investigated. The emission legislation is however very diversified in different countries; a short summary of the legislation in the EU, the USA and Brazil is presented in this study. In the EU regulations, everything measured with the FID (Flame Ionization Detector) is treated as hydrocarbon emissions. In the USA the alcohols and aldehydes are measured and reported separately from hydrocarbons. In Brazil, the alcohol part can be measured separately on voluntary basis. The influence of some of these differences has been further investigated in this report. Results from two related studies are presented. The FID response for ethanol was investigated and emission testing of an E85-fuelled FFV (Flex Fuel Vehicle) was performed.

Clean combustion is one of the inherent benefits of using a high methane content fuel, natural gas or biogas. A single carbon atom in the fuel molecule results, to a large extent, in particle-free combustion. This is due to the high energy required for binding multiple carbon atoms together during the combustion process, required to form soot particles. When scaling up this process and applying it in the internal combustion engine, the resulting emissions from the engine have not been observed to be as particle free as the theory on methane combustion indicates. These particles stem from the combustion of engine oil and its ash content. One common practice has been to lower the ash content to regulate the particulate emissions, as was done for diesel engines. For a gas engine, this approach has been difficult to apply, as the piston and valvetrain lubrication becomes insufficient.