COLUMBUS, Ind. – Cummins, working with the Propane Education
and Research Council (PERC), has developed a medium-duty propane demonstration
engine that it claims will outperform diesel in key areas.
Based on its B6.7 diesel, the 6.7 LPG direct injection
engine could be well suited for a range of medium-duty applications, offering a
20-40% cost savings over 10 years compared to a diesel with similar displacement
and torque curve.
That savings, of course, is heavily dependent on diesel and
propane prices, but PERC and Cummins also say the new design for the first time
offers performance matching or exceeding diesel in several key areas such as
torque and power output.
The project began with a trade show booth visit in 2014,
recalled Cinch Munson, senior vice-president, business development with PERC.
After discussing the merits of propane with Cummins, the program was officially
launched in 2016.
“The goal was to develop an advanced concept that leverages
the performance of the fuel,” said Sam Geckler, product line architect with
Cummins. After hundreds of hours of design, and thousands more in simulations,
an LPG engine offering “diesel engine-like performance” was developed.
Some of the features include a high compression ratio, an
aluminum cylinder heard, and a purpose-built fuel system. Many of the base
components were carried over from the B6.7 diesel. The first engine was
installed in Peterbilt 337, initially fitted with a flatdeck to allow easier
access to components, but later converted to a propane bobtail delivered to AmeriGas
for real world testing.
The truck has put on about 8,000 miles, the last 2,000 of
which were fully loaded delivering propane around Bloomington, Ind.
The project is currently at the “demonstration level,” said
Geckler, adding “that doesn’t mean concept level, where you only build one. We
built multiple engines and we are now ready to go off and show what this engine
can do in a vehicle in the field.”
Saradhi Rengarajan, technical project leader with Cummins,
said the most exciting aspect of the project was the torque the designers were
able to achieve. Peak torque is 900 lb.-ft., far exceeding propane engines
already in the market.
The efficiency of the engine has also led to favorable
emissions performance, with CO2 emissions 11% less than a diesel, Rengarajan
noted, while traditionally LPG engines had greater CO2 output than diesels. He
said the 6.7L LPG offers a 28% improvement in CO2 output compared to propane
engines in the market today.
Part of that CO2 improvement came from optimization of the
combustion system, which allowed Cummins to avoid exhaust gas recirculation
(EGR). The biggest challenge designers had to overcome when testing the engine
was related to injector failures, which caused the company to adopt a vapour
phase injection (VPI) system, sacrificing up to 1% in thermal efficiency in
exchange for greater reliability.
But Rengarajan said the VPI system has performed well, even
with cold starts at 10F or colder, alleviating a significant concern regarding
vapour systems.
As for when we may see the Cummins 6.7 LPG engine in the
market, more analysis will first have to be done to determine the market demand.
“Cummins would require further inputs on the market needs
and the business case to commit to a product development and commercialization
program,” the company said in response to a question about future availability.
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