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The Structure and principle of the hydraulic free piston engine (HFPE) is analyzed, and the mathematical model is established according to the feature of the working principle. The transient processes are analyzed through simulation. The result shows that: 1) the working cycle of the HFPE is unsymmetrical, the compression stroke time is 16ms and the expansion stroke time is 10ms. 2) The speed of the power piston is faster than the conventional diesel engine, the maximum speed in the compression stroke is 12m/s and the maximum speed in the expansion stroke is 17m/s. 3) The acceleration is bigger than the conventional engine, the maximum value is 16500m/s2, at the top dead centre and the smallest value is 3500m/s2 at the bottom dead centre.

Knock in gasoline engines at higher loads is a significant constraint on torque and efficiency. The anti-knock property of a fuel is closely related to its research octane number (RON). Ethanol has superior RON compared to gasoline and thus has been commonly used to blend with gasoline in commercial gasolines. However, as the RON of a fuel is constant, it has not been used as needed in a vehicle. To wisely use the RON, an On-Board Separation (OBS) unit that separates commercial gasoline with ethanol content into high-octane fuel with high ethanol fraction and a lower octane remainder has been developed. Then an onboard Octane-on-demand (OOD) concept uses both fuels in varying proportion to provide to the engine a fuel blend with just enough RON to meet the ever changing octane requirement that depends on driving pattern.

The spark ignition engine particulate number (PN) emissions have been correlated to a particulate matter index (PMI) in the literature. The PMI value addresses the fuel effect on PN emission through the individual fuel species reactivity and vapor pressure. The latter quantity is used to account for the propensity of the non-volatile fuel components to survive to the later part of the combustion event as wall liquid films, which serve as sources for particulate emission. The PMI, however, does not encompass the suppression of vaporization by the evaporative cooling of fuel components, such as ethanol, that have high latent heat of vaporization. This paper assesses this evaporative cooling effect on PN emissions by measurements in a GDI engine operating with a base gasoline which does not contain oxygenate, with a blend of the gasoline and ethanol, and with a blend of the gasoline, ethanol, and a hydrocarbon additive so that the blend has the same PMI as the original gasoline.