Paper Review By Longxiang Liu Apr. 9, 2015 The Research and Motor octane numbers of Liquefied Petroleum Gas (LPG) Kai J. Morganti Paper Review By Longxiang Liu Apr. 9, 2015

Motivation Liquefied Petroleum Gas (LPG) is a mixture primarily comprised of propane, propylene and the butanes. In liquid form, it has an energy density comparable to other liquid hydrocarbon fuels and its combustion results in lower emissions of regulated pollutants and greenhouse gases. Currently, the MON of LPG is assumed to be a compositionally weighted linear sum of MONs of its pure constituents which is not clear to be reasonable for all LPGs. And no corresponding method to determine the RON of LPG. RON is considered to be more relevant to modern SI engines and specified in fuel quality standards for gasoline.

Objective Obtain a comprehensive set of octane number data for LPG mixtures using test methods consistent with the ASTM methods for liquid fuels. Develop an octane number model for LPG with respect to fuel composition. Evaluate the existing fuel standards for LPG. Implications for the design of future LPG quality standards.

Experimental Methods Develop an additional sample fuel preparation system and modify the standard intake hardware to measure octane numbers of gaseous fuels Run CFR engine on the test fuel at either the motor or research operation conditions. Slowly increase CR until the standard amount of knock occurs (measured with ASTM knock meter-responds to rate of pressure rise) At that compression ratio, run the engine on blends of reference fuels (iso-octane and n-heptane) The octane number is the liquid volume percentage of iso-octane in the blend that produces the standardized knock at that CR.

Octane number model for LPG

Octane number model for LPG RON data MON data Octane numbers of these mixtures is generally non-linear with respect to composition. The presence of propylene is the major source of non-linearity in the RON. The MONs are generally more linear than the RONs.

Current Fuel Standards Australian Fuel Determination Fixed vapor pressure limits of 800 kPa and 1530 kPa (at 40 ℃) and minimum MON requirement of 90.5 European EN589 standard Variable lower vapor pressure ranges from 275 kPa to 950 kPa to account for seasonal variations. The upper vapor pressure limit is 1550 kPa. Minimum MON requirement is 89.0 United States Propane HD-5 Fuels comply with this standard contain at least 92.5% (vol/vol) propane. Maximum concentration of propylene and heavier hydrocarbons is 5% and 2.5%

Implications for fuel quality standards These current standards constrain the RON of LPG to be significant higher than that of standard gasoline in all cases, whilst the minimum MON is also significantly higher than that of most gasolines. This suggests that relaxation of both the RON and MON requirements of LPG is possible. Further, LPG fuelled engines which inject liquid fuel into the port or directly into the cylinder are becoming more common. If this trend continues, such that liquid phase injection dominates the market, the lower vapor pressure limit of LPG’s may also be reduced or even eliminated. Relaxation of both the minimum octane number and minimum vapor pressure requirements of LPG may then enable significant environmental and economic benefits. Of course, further research is needed to establish the actual performance of these fuels in modern production engines before such recommendations can be made with confidence.

Questions?