Sean Bennett Diesel engines, trucks, and off-road equipment

March 9, 2019

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Filed under: — techrite @ 5:47 pm

March 9th 2019 

ALL-ELECTRIC DRIVETRAINS

Today every truck OEM in North America is either producing or experimenting with all-electric vehicles. In this respect, we lag behind the rest of the world where commercial electric vehicles have a much better established commercial market. So far, the world’s most successful automobile EV (to date) is the Nissan Leaf: the 2019 version of this compact automobile claims a 200 mile range and given that a recent survey suggests that the average American drives 38 miles a day, this will satisfy many urban driver’s requirements.

Commercial vehicles are different. Because they are work machines, they are required to operate throughout a typical working day so the challenge is to have sufficient electrical storage density to achieve this without risk of stranding the vehicle. This means that offshore manufacturers have leveraged an advantage in our market due to their use of electric powertrains for a generation. To reinforce this, FedEx has recently announced the acquisition of 1,000 panel vans from China’s Chanje.

Energy density is all about battery capacity. However, improvements in Li-ion batteries in the very recent past are making possible trucks such as the BYD Bay area refuse packer shown at the beginning of this blog. LMC, LTO, and LFP are currently favored by OEMs. Referencing the BYD garbage packer again, it should be pointed out that the electric load requirements on a vocational truck of this type given its considerable hydraulic requirements.

Domestic E-Trucks

While domestic transit E-buses are becoming a common sight in cities, E-trucks are much talked about, but less likely to be seen on our roads. Major challenges have focused on energy density (ie range) and E-component cooling. Nothing beats the experience of monitoring and responding to technical problems in real-world, over-the-road scenarios, and this has provided Chinese and European electric commercial vehicles with an advantage. Here is a list of all-electric and fuel cell Class 6-8 trucks seen on our roads that have progressed beyond a prototype phase:

  • BYD 8TT
  • Cummins Roush AEOS
  • Daimler eCascadia (based on MB eActros)
  • Daimler eM2
  • Daimler Fuso eCanter
  • Navistar-VW eClass 6
  • Nikola One
  • Paccar Kenworth-Toyota FC T680 (fuel cell)
  • Paccar Peterbilt 220 EV
  • Tesla Semi
  • Volvo FE

Natural Gas Basics

Inhabitants of cities from San Diego to Vancouver have become accustomed to seeing signage such as “Powered by Clean Natural Gas” on transit vehicles for a generation. In many cases, hybrid electrical power is used on the West Coast but unlike their counterparts in East Coast cities, the power source is more often a natural gas (NG) fueled- rather than a diesel-fueled engine.

The core constituent of NG is methane. Unlike diesel fuels which are typically composed of a complex chain of carbon and hydrogen atoms, methane has a simple chemical constitution consisting of a molecule in which a single carbon atom bonds with four hydrogen atoms. As a result, it tends to be relatively clean burning providing it is in a pure state. Although what we call NG is primarily methane, it can also contain other not so simple petro-chemicals such as propane, ethane, and butane – because NG is sourced from petroleum reserve or refinery boil-off. This chemical variability of NG can cause operational problems. The U.S. and Canada have sustainable NG resources: but outside of West Coast cities, the retail and distribution infrastructure is poor.

Methane in its pure form is a ‘clean’ fuel and depending from where it’s sourced, it can also be a ‘green’ fuel. It has three main sources: the first is NG, the second is from natural fermentation of vegetable matter (wetlands, etc), and the third is from landfill sites, where it is known as landfill gas (LFG). Because the U.S.A. and Canada are blessed with plenty of geographical space, we have the most primitive garbage handling infrastructure in the developed world: Most of our LFG emission from rotting garbage discharges to atmosphere where it can be defined as undesirable greenhouse gas (GHG). The Europeans and especially the Scandinavians have developed a garbage handling infrastructure which captures LFGs. Once captured, LFGs can be purified (removing sulfur and carbon dioxide) and the resulting methane used to fuel vehicles. It is likely to be some time before we have the capability to capture methane from LFGs because the investment in infrastructure and purification plants is significant and usually not within the budgets of our city corporations which handle most of our garbage. At present, it is easier to dump garbage on land that is perceived as having lesser value.

So, that leaves us with NG at least for the immediate future. It is commercially available in two forms. The first is liquefied natural gas (LNG). LNG is a cryogenic liquid which must be stored at temperatures of -238 degrees F (-150 degrees C) or less to prevent it boiling off as a gas. It is can be stored at pressures of around 230 psi (16 bar). The second is compressed natural gas (CNG). CNG is stored in gaseous form but this must be at pressures ranging from 3600 to 5000 psi (250 to 345 bar) requiring special high pressure storage vessels.

NG has low energy density in both its formats. For instance, diesel fuel has an energy density of 1058 Btus (267 kilo calories) per cubic foot – compared with 266 Btus (67 kilo calories) for CNG. This means that it’s unlikely that it will ever be truly practical as fuel for linehaul trucking operations: But that said, it is already used in some class 8 trucks operating short haul.

To this point in time, all commercial vehicle NG-fueled engines are adapted diesel engines. Because NG will not auto-ignite under normal diesel engine compression temperatures, some assistance is required. This can be provided in three ways:

• Diesel fuel pilot pulse
• Hot surface ignition (continuously energized glow plug)
• Spark ignition

Another problem with NG fuel usage is that while particulate matter (PM) is eliminated, it produces higher NOx emissions when combusted: this has actuallyreduced the number of manufacturers offering NG fuel systems since EPA 2010. Over the years, Westport Innovations has emerged as a leader in engineering NG fuel systems into commercial vehicle engines. Westport fuel injectors for both LNG and CNG fuel delivery are used by their partner OEMs, especially Cummins. Two current Westport injectors are:

• High-pressure direct injection (HPDI) for LNG: the HPDI is a common rail dual-fuel (diesel fuel is used for pilot ignition, LNG as the primary fuel) with piezo actuators.
• Mono direct injection (MDI) for CNG: MDIs inject the CNG charge and hot surface (usually a glow plug) ignition is required.

Another disadvantage of NG fuel usage at least from a trucking perspective, is that specialized engine lubes along with more frequent servicing is required. This, and the fact that NG degrades more rapidly than diesel fuel under storage conditions, reduces its appeal to any type of truck activity that operates beyond inner city boundaries. For the moment, NG has to be regarded as a fuel to be used for short haul, intra city vehicles.

 Some technical data in this article is sourced from TMC S.11 Energy Conservation Group Tech Sessions. More detailed information on NG and other alternate fuel systems can be found in the 5th Edition of Medium/Heavy Duty Truck Engines, Fuel, and Computerized System Management available from Delmar Cengage Learning.

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