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Power Torque Magazine (AU)  /  March 2017

Is CNG or LNG the alternative answer to rising fuel costs? Chris Mullett reports from Louisville, Kentucky.

According to the commodities experts, the United States could well become an exporter of natural gas by the end of 2014, ending the nation’s reliance on foreign imports. But does the newfound wealth of the gas drillers produce a global solution for transport operators looking for an alternative to diesel fuel?

When America has a problem it also has a habit of letting the solution it comes up with override any full critique. It often seems to be a case that the end justifies the means.

The latest expansion of the coal seam gas exploration industry, taking place all over America, looks at first sight as though it is the panacea for unemployment. Could this be the rapid way for the nation to reduce a budget deficit of alarming proportions and at the same time provide the means to kick-start the US economy?

The drillers obviously say yes. The methods used in the extraction process of “fracking” requires thousands of new trucks to haul equipment, plus tankers to carry the water and chemicals used to pump under ground to fracture the substructure.

As the nation taps into the gas boom, it’s all systems go for the natural gas exploration industry. And while your company is drilling for gas and finding plenty of reserves that require very little in the way of refining to make it usable, why not run your vehicles on the stuff? After all, it’s up to half the price of petrol and it’s clean as far as emissions regulations are concerned.

The only drawback to all this excitement is that we seem to have very little knowledge available as to how the ground will react to what is taking place sometimes thousands of feet below. Whether the toxins released by the fracking process can seriously damage the environment, turning the ground barren and poisoning water, appears to be a possibility. But all this is lost or forgotten in the search for financial gain.

For Westport Innovations Inc. the availability of clean gas has led to the company developing advanced technology natural gas and liquefied petroleum gas (LPG) engines, fuel systems, and components for the original equipment manufacturer (OEM) light-duty automotive and industrial markets.

CNG at the pump is close to half the price of diesel or petrol in the US. While there are currently fewer natural gas fuelling stations than traditional petrol stations, the natural gas station numbers are growing, and it’s now possible to do a long-haul trip entirely on natural gas.

The media spin for the gas industry is all about clean energy. One distributor alone has already added 150 LNG refuelling sites across America in the past year, and there are currently 23 LNG and 39 CNG sites up and running in Texas alone. Not surprisingly, the drilling companies proudly operate their light, medium and heavy-duty trucks on CNG, LNG or a combination of either fuel with petrol or diesel.

The decision to convert to CNG is obviously based on overall whole-of-life costs. In the American example, where the CNG purchase price is half that of petrol, this is factored in against the cost of the original conversion.

Recognising the advantages of running medium-duty and heavy-duty trucks on gas has brought Cummins into the equation with its new ISX12G engine and its existing ISL G engine.

Introduced in 2007, the ISL G is an 8.9-litre, six-cylinder, spark-ignition engine that shares the same full-skirted block as the Cummins ISL 9 diesel for increased rigidity and strength. The design provides superior piston ring and bearing life, improved coolant flow and targeted piston cooling, for greater reliability and superior durability. Life-to-rebuild and rebuildability are similar to those of diesel engines.

The ISL G is available in power ratings of 186-239 kW (250-320 hp) and with peak torque outputs ranging from 990-1,356 Nm (730-1000 lb-ft) rated at 2,200 rpm.

With a displacement of 11.9 litres, the new six-cylinder ISX12 G is available in power ratings of up to 298 kW (400 hp) and 1,966 Nm (1,450 lb-ft) of torque.

The engine features stoichiometric cooled exhaust gas recirculation (EGR) combustion technology and spark ignition, and a simple three-way catalyst aftertreatment. It does not require a Diesel Particulate Filter (DPF) or Selective Catalytic Reduction (SCR) treatment.

The ISX12 G is a dedicated natural gas engine that’s based on the Cummins ISX12 diesel but that operates on 100 percent natural gas.

The natural gas fuel itself can be stored in either compressed form (CNG) or in liquefied form (LNG). The engine can also operate on biomethane that meets fuel quality standards.

Higher up the power and torque range is the Westport 15L. Optimised for the heavy haul and waste disposal markets, this 15-litre, LNG-fuelled engine is available in power ratings of 298-354 kW (400-475 hp) and with peak torque ratings of 1,966-2373 Nm (1,450-1,750 lb-ft).

This engine uses Selective Catalytic Reduction (SCR) aftertreatment to achieve a claimed fuel economy gain of five percent compared to non-SCR alternative engines.

All the North American truck makers currently have some form of LNG and CNG alternative for their customers. Most rely on the expertise of Cummins, with manufactures such as Volvo and Mack adding their own D13 based LNG-fuelled engine.

The D13, unlike the Cummins alternative, is a compression ignition engine where pilot injection of diesel is closely followed by an injection of LNG. Because of the need for liquefied gas injection, it will not operate on CNG.

Volvo and Mack claim a 10-20 percent improvement in fuel economy when compared to a spark ignition alternative, with the engine producing 334 kW (455 hp) and 2,373 Nm (1,750 lb-ft) of torque. That said, the D13 LNG engine will not be available on the US market until mid to late 2014.

No doubt there are some interesting options developing for LNG and CNG use in transport.

The main users at this stage remain those employed in the waste industry or mass transit. But it should be remembered that, although the LNG and CNG option appears to be a high topic for discussion, the current use of these fuels in transport accounts for less than one percent of the vehicle pool.

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Good article.  My employer is going to CNG in a very big way, primarily because we are a natural gas/electric utility, but also because we are seeing a significant rise in the operating costs of diesel powered trucks.  Does it make financial sense?  I can't answer that conclusively at this point, I don't have all of the pertinent information and you never really know until the end of the vehicle's life cycle, but it looks promising.  Mechanics and drivers like CNG, and that's always a plus.

As for Cummins and Westport, I don't think conversions of compression-ignition engines to spark-ignition gaseous fuel engines is a good solution.  They do have an advantage in that they integrate into chassis set up for equivalent diesel engines easily, but I think they are too heavy and inefficient.  A decent short-term solution until we see if there is a market for a purpose-built heavy duty CNG/LNG engine.  I think the PSI 8.8L and 10.4L V-8's are closer to the ideal CNG/LNG engine.

Volvo/Mack's D13 LNG engine sounds a little bit like Detroit Diesel's unsuccessful PiNG engine.   



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