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Adoption of high-pressure common-rail (HPCR) fuel systems, which subject diesel fuels to higher temperatures and pressures, has brought into question the veracity of ASTM International specifications for biodiesel and biodiesel blend oxidation stability, as well as the lack of any stability parameter for diesel fuel. A controlled experiment was developed to investigate the impact of a light-duty diesel HPCR fuel system on the stability of 20% biodiesel (B20) blends under conditions of intermittent use and long-term storage in a relatively hot and dry climate. B20 samples with Rancimat induction periods (IPs) near the current 6.0-hour minimum specification (6.5 hr) and roughly double the ASTM specification (13.5 hr) were prepared from a conventional diesel and a highly unsaturated biodiesel. Four 2011 model year Volkswagen Passats equipped with HPCR fuel injection systems were utilized: one on B0, two on B20-6.5 hr, and one on B20-13.5 hr.

Over the next decades to come, fossil fuel powered Internal Combustion Engines (ICE) will still constitute the major powertrains for land transport. Therefore, their impact on the global and local pollution and on the use of natural resources should be minimized. To this end, an extensive fundamental and practical study was performed to evaluate the potential benefits of simultaneously co-optimizing the system fuel-and-engine using diesel as an example. It will be clearly shown that the still unused co-optimizing of the system fuel-and-engine (including advanced exhaust after-treatment) as a single entity is a must for enabling cleaner future road transport by cleaner fuels since there are large, still unexploited potentials for improvements in road fuels which will provide major reductions in pollutant emissions both in vehicles already in the field and even more so in future dedicated vehicles.

An investigation was conducted to elucidate, how the latest turbocharged, direct injection Volkswagen diesel engine generation with cylinder pressure based closed loop control, to be launched in the US in 2008, reacts to fuel variability. A de-correlated fuels matrix was designed to bracket the range of US market fuel properties, which allowed a clear correlation of individual fuel properties with engine response. The test program consisting of steady state operating points showed that cylinder pressure based closed loop control successfully levels out the influence of fuel ignition quality, showing the effectiveness of this new technology for markets with a wide range of fuel qualities. However, it also showed that within the cetane range tested (39 to 55), despite the constant combustion mid-point, cetane number still has an influence on particulate and gaseous emissions. Volatility and energy density also influence the engine's behavior, but less strongly.

In this paper the emissions of regulated and unregulated exhaust gas components of a fleet of diesel passenger cars measured at Volkswagen in the eighties are compared with the results of a new investigation on modern direct-injection diesel vehicles. The potential of improved diesel fuels to reduce emissions is also examined. The emissions of regulated exhaust gas components as well as fuel consumption have been reduced significantly in the last years as a result of the systematic further development of conventional swirl chamber engines and exhaust gas after-treatment as well as the introduction of SDI/TDI engines. As was to be expected, this has also had a positive effect on the emissions of unregulated exhaust gas components. It has been possible, for example, to reduce the polycyclic aromatic hydrocarbons adsorbed on diesel particulates by more than 95%.