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Two single-cylinder diesel engines were optimised for advanced combustion performance by means of practical and cumulative hardware enhancements that are likely to be used to meet Euro 5 and 6 emissions limits and beyond. These enhancements included high fuel injection pressures, high EGR levels and charge cooling, increased swirl, and a fixed combustion phasing, providing low engine-out emissions of NOx and PM with engine efficiencies equivalent to today's diesel engines. These combustion conditions approach those of Homogeneous Charge Compression Ignition (HCCI), especially at the lower part-load operating points. Four fuels exhibiting a range of ignition quality, volatility, and aromatics contents were used to evaluate the performance of these hardware enhancements on engine-out emissions, performance, and noise levels.

Future vehicles will increasingly be required to improve their efficiency, reduce both regulated and CO₂ emissions, and maintain acceptable levels of driving, safety, and noise performance. To achieve this high level of performance, they will be configured with more advanced hardware, sensors, and control technologies that will also enable their operation on a broader range of fuel properties. These capabilities offer the potential to design future vehicles to operate on the most widely available and GHG-reducing fuels. In previous studies, fuel flexibility has been demonstrated on a compression ignition bench engine and vehicle equipped with an advanced engine management system, closed-loop combustion control, and air-path control strategies. An unresolved question is whether engines of this sort can operate routinely on market gasoline while achieving diesel-like efficiency and acceptable emissions and noise levels.