PERC is funding a number of research projects to evaluate the performance of propane Autogas in a range of internal combustion engines. These projects are primarily run on engine dynos – test rigs where the engines are tested outside of a vehicle – at research organizations in order to accurately assess and quantify the performance of these engines when operating on Autogas.

All of the projects are either in the initial set-up phase or not yet started, so this report is more about what we will be doing rather than results. The actual results will follow in future months and will be the subject of a later report (if not multiple reports).

Current US Autogas market trends
It is worthwhile to look first at the current market for Autogas-powered vehicles in the United States.  The country has an unusual market dynamic when compared with the rest of the world in that big, gasoline spark-ignited (SI) engines comprise a large percentage of light- to medium-duty commercial vehicle fleets. These so-called “Detroit Iron” engines – large displacement V8s (and V10s) operating on gasoline — are alive and thriving in commercial vehicles, even as they slowly decline in numbers among privately-owned vehicles.  The conversion of these Detroit Iron fleet vehicles to Autogas (both dedicated and bi-fuel) is being achieved with a mixture of direct Original Equipment Manufacturer (OEM) released, OEM approved and pure aftermarket products.

This market has been an easy target for Autogas (and compressed natural gas) aftermarket conversions because converting a SI gasoline vehicle to a SI Autogas vehicle is relatively straightforward and the payback is relatively quick as fuel consumptions in such  vehicles is high. However, the Detroit Iron still has a size limit —about 8 litres, with engines that are all naturally aspirated. These engines can generate more than enough power but insufficient torque for the larger medium-duty and heavy-duty truck products and for transit buses.

At the opposite end of the on-highway vehicle spectrum, conversions of passenger cars and sports utility vehicles (SUVs) have been limited to public service vehicles, such as police cars, limousines and taxis.  These markets had been dominated by a number of Ford products, all using the same 4.6 litre V8 engine. However, production on this engine stopped two years ago, leading to a vacuum in the market that all manufacturers are trying to fill. Unlike in Europe, private owner conversions of light duty vehicles are uncommon because gasoline in the United States is still relatively inexpensive.

Heavy-duty on-highway engines
There are several research projects underway evaluating technology which could lead to Autogas being used in the higher torque engines necessary for the heavy-duty market.

Compression-ignition dual-fuel technology
This project will evaluate the performance of a dual fuel system – the addition of a secondary Autogas fuel system to an existing compression ignition diesel engine, such that the Autogas replaces some of the diesel but still ignites with compression ignition. As part of a project being undertaken at Mississippi State University, a 13 litre in-line six-cylinder (I6) engine will be fully tested on an engine dyno over a wide range of engine speed and power conditions, with a number of secondary Autogas fuel supply alternatives. The electronic controller for the engine  in this project is a full open-access research-grade system, which has already demonstrated a duplication of the base diesel engine performance compared to what was achieved using the original standard controller. The research controller will permit full variability of base diesel injection (including timing and the number of injections), boost control and the exhaust-gas recirculation (EGR) flow rates, along with the timing and quantity of the substitute Autogas.  Full emissions are being measured on this project and the results will quantify the potential diesel substitution rates with this technology, as well as the resulting impact on the engine emissions from diesel substitution.

In a related project, a number of aftermarket Autogas systems will be tested on a Navistar 466 7.6 litre diesel engine to gauge their market potential.

Heavy-duty spark-ignited boosted engine technology
In the heavy-duty on-highway market today, there are a number of spark-ignited, boosted engines that only operate on natural gas. These engines are modified I6 compression ignition engines that have been converted to spark ignition, basically replacing the diesel direct injector with a spark plug and a reduction in the compression ratio as the major changes.  These engines are typically optimized for compressed natural gas (CNG) as this has been the main market for this product.  The higher octane rating of natural gas over Autogas has historically kept the maximum torque performance of the Autogas versions below that of the natural gas equivalent engine – particularly when the engine is mechanically optimized for natural gas.

The research project will take an existing CNG-optimized spark-ignition engine and modify it so that Autogas can be introduced through a multi-point (port) liquid injection (LPI) system rather than the gaseous single-point system found in CNG engine systems. Depending on the results from this work, other changes such as a further drop in the compression ratio will then be evaluated.   The test work will be undertaken on an engine dyno, again with a full access engine controller, with emissions and performance measured for both the base CNG configuration and the LPI system. 

Light-duty on-highway engines
Although only a small proportion of light-duty vehicles in the United States are able to run on Autogas, the significant advantages of Autogas over CNG – minimal reduction of vehicle luggage /freight capacity, the lighter weight of the fuel tank and the ready availability of refuelling infrastructure – makes Autogas a much more viable alternative fuel option for light duty vehicles. Combined with these advantages, direct injection, a technology that Autogas is ideally suited to, is now being adapted by the OEMs in their light-duty vehicles as they strive to meet increasingly stringent fuel-consumption targets. Research in Europe and Asia has demonstrated some of the emissions benefits that can be achieved with direct injection of liquid propane (LPG), in particular the significant reductions in emissions of particulate matter (PM). Emission standards for PM do not yet exist for spark-ignition engines, but will be introduced with Euro 6 and California LEVIII standards.  

Spark-ignition direct injection (SIDI) engine technology
This project, which makes use of both engine dynamometer and vehicle chassis test facilities, has multiple aspects. The work will assess engine performance in both naturally and boosted SIDI engines and engine durability on engine dynos, and test a typical US SIDI fleet vehicle operating on Autogas over standard US emission test-cycles.

The test vehicle is a GM Caprice (sold only as a police vehicle in the United States) with a 3.6 litre SIDI V6 engine that has been converted with an available European aftermarket system to a bi-fuel gasoline/Autogas system. Preliminary testing of this vehicle is due start by the end of 2012.

Engine dyno testing on the boosted SIDI engine is scheduled to commence in January 2013. This will entail mapping on gasoline and Autogas under part- and full-load conditions, and an evaluation of engine warm-up emissions/catalyst light-off performance – operating conditions where port-injected Autogas engines have been shown to give significant benefits over gasoline in similar tests. 

Dyno testing of the naturally aspirated SIDI engine has still to be finalized: a late project “wish” has been added involving an attempt to run the engine durability phase at the actual fuel system supplier’s engine test facility. 

Advanced research projects
In addition to these research projects, which could readily turn into development projects, there are also a number of longer term projects either in progress or in the project development phase.

Low-temperature combustion
This project is in progress at Mississippi State University (the Dual Fuel Evaluation project being the first phase of this project). The next phase will entail the low-temperature combustion of a lean Autogas-air mixture by appropriately timed diesel fuel injection. The predominantly lean combustion of Autogas will ensure very low PM emissions, and the resulting low temperature of combustion will result in very low nitrogen oxide (NOx) emissions. This will be achieved while keeping conventional diesel-engine like thermal efficiencies. The objective of this phase will be to determine how much of the engine speed and power conditions can be operated in this low-temperature combustion regime.

Advanced SIDI evaluations
The SIDI test work described above is aimed at the light-duty vehicles currently operating on SIDI. Future projects will look to generate data on what today’s SIDI engines could achieve if operating in lean-burn mode, with potential for off-highway applications. A second project will investigate Autogas SIDI in heavy-duty engines. This would require major changes in today’s heavy-duty engines, as both a spark plug and a direct injector in the cylinder head would be needed.  

Partnerships
PERC is the main funding source for the projects described above, but is always interested in partnerships where other entities – be they OEM’s, tier-1 suppliers, fuel-supply industry, academia or other market development entities – would share in the project concepts, project development, workload and, ultimately, the results.

To find out more about developments in Autogas engine technology, please contact Alan McEwan at alan.mcewan@propane.com, or visit the following websites: www.autogasusa.org, www.usepropane.com and www.propanecouncil.org.