Analysis of LPG fuels

Owing to their CO2 reduction potential and their high knock resistance, gas fuels such as LPG (Liquefied Petroleum Gas) are well suited for the operation of modern highly charged gasoline engines. When adapting the prevailing LPG fuel standard EN 589 to modern engine concepts, the influence of substance properties and the gas composition on the fuel injection behaviour must, however, be scientifically tested. Experimental tests on four selected LPG fuel mixtures according to EN 589 thus form the basis of this research project. On the project, a 1.6- litre turbocharged spark ignition engine with direct fuel injection and a high pressure pump/injector wear test stand were used. Important information about the maximum propane content and the wear behaviour of the injector as well as the high-pressure fuel pump could be derived from this. The project may significantly contribute to the LPG standardisation process in Europe (CEN) and Germany (DIN) and thus to further establishing LPG as an alternative fuel.

» A thorough understanding of the effect of LPG fuel properties on the operating behaviour of contemporary gasoline engines is an important prerequisite for guaranteeing the fuel quality using fuel standards. As shown in both FVV LPG projects, introducing limits for maximal and minimal propane content as well as new figures for evaluating LPG knock resistance, for example the methane number, is essential in order to meet future CO2 targets. We can only hope that the knowledge gained through the FVV projects will lead the standardisation committees to quickly agree on a forward-looking definition for fuel quality. «
Dr.-Ing. Ulrich Kramer | John Andrews Research Centre (Ford-Werke GmbH)

Gas fuels such as LPG are a promising fuel alternative for gasoline engines.

Photo Credit: Fotolia | Albina Glisic

The high vapor pressure of C3 and C4 hydrocarbons in Liquefied Petroleum Gas (LPG) can induce fuel evaporation in the high or low pressure side of the high pressure pump (HPP) of an LPG direct injection system. This results in rapid density reduction and thus engine stall. Within the scope of the FVV project LPG Direct Injection executed at the VKA at the RWTH Aachen University and the IAP at the University of Applied Sciences Saarland the supercritical fuel state has been investigated as a potential solution for advanced LPG direct injection systems for modern spark ignition engines without any fuel cooling measures.

Photo Credit: Fotolia | LianaM

Relation between required inlet pressure on the high-pressure pump and the propane/propene content of all LPG fuels.

Photo Credit: FVV | VKA

A test vehicle with a 1.6 litre gasoline engine was used for the tests.

Photo Credit: IAP | htw saar

Motivation

Owing to their CO2 reduction potential and their high knock resistance, gas fuels such as LPG (Liquefied Petroleum Gas) are well suited for the operation of modern spark ignition engines. For a wider use of LPG fuels, it is, however, necessary to update the European LPG fuel standard EN 589 with regard to modern engine concepts. For this to happen, knowledge must be gained about the impact of fuel properties and the gas composition on the engine combustion behaviour of these gas fuels.

Methodology

Experimental tests with four LPG fuel mixtures that meet existing standards formed the basis of this project. Tests were conducted on a 1.6-litre turbocharged direct fuel injection gasoline spark ignition engine, a one-cylinder research aggregate, a high-pressure pump/injector test stand as well as a test vehicle with a 1.6-litre spark ignition engine with direct fuel injection. A detailed analysis of the influence of the substance properties of LPG near the critical point on the direct injection was the focus of the tests. This also included a comparison of the injection behaviour of the different LPG aggregate states (subcritical – supercritical).

Result

It is useful to restrict the propane/propene content of future LPG fuels to a maximum of 70 % (m/m) for any LPG direct injection concepts with a conventionally designed high-pressure fuel pump. For LPG fuels with a maximum propane content of 70 % (m/m), it could be shown that the function of the high-pressure fuel pump with an inlet pressure of 45 bar can be guaranteed – even at fuel temperatures nears the critical point, and thus at greater compressibility. The propane rate should, nevertheless, be as high as possible, as corresponding LPG fuels have proven to be extremely robust against pre-ignition and glow ignition. Significant injector wear only shows in operation with supercritical LPG. Compared with liquid operation, the high-pressure fuel pump showed greater pump piston wear in both subcritical and supercritical LPG.

On the one hand, the findings contribute to the LPG standardisation process in Europe (CEN) and Germany (DIN), and on the other hand, to further establishing LPG as an alternative fuel.

Documentation

LPG System Comparison I | Comparison of the thermodynamic potential, the octane requirement and the contamination tendency of three LPG concepts in a turbocharged direct injection gasoline SI engine: LPG-DI, LPG-PFI (liquid) and LPG-PFI (gaseous) | Project No. 1069

LPG System Comparison II | Investigation of the effect of supercritical LPG on combustion phenomena and hot fuel handling issues in LPG DI systems | Project No. 1151

Themis

Status
Finalised

Programme
FVV Funding

Budget
836.844,00 EUR

Time Period
2011-06-01 to 2013-07-31 Part I
2013-08-01 to 2016-01-31 Part II

Funding Organisations