Editing Auxiliary power unit (section)

==Commercial vehicles==
A refrigerated or frozen food semi trailer or train car may be equipped with an independent APU and fuel tank to maintain low temperatures while in transit, without the need for an external transport-supplied power source.{{Citation needed|date=July 2014}}<ref>{{Cite web|url=http://www.ooida.com/EducationTools/Info/weight-exemptions.asp|title=Vehicle weight exemptions for APUs}}</ref>

On some older diesel engined-equipment, a small gasoline engine (often called a "pony engine") was used instead of an electric motor to start the main engine. The exhaust path of the pony engine was typically arranged so as to warm the intake manifold of the diesel, to ease starting in colder weather. These were primarily used on large pieces of construction equipment.<ref>{{cite book|last1=Orlemann|first1=Eric|title=Caterpillar Chronicle: History of the Greatest Earthmovers|isbn=9781610605779|pages=35}}</ref><ref>{{cite web|title=Willard v. Caterpillar, Inc. (1995)|url=http://law.justia.com/cases/california/court-of-appeal/4th/40/892.html|website=Justia Law|access-date=13 December 2016}}</ref>

===Fuel cells===
{{main|Fuel cell auxiliary power unit}}
In recent years, truck and fuel cell manufacturers have teamed up to create, test and demonstrate a fuel cell APU that eliminates nearly all emissions<ref>{{cite news|first=Christie-Joy |last=Broderick |author2=Timothy Lipman |author3=Mohammad Farshchi |author4=Nicholas Lutsey |author5=Harry Dwyer |author6=Daniel Sperling |author7=William Gouse |author8=Bruce Harris |author9=Foy King |title=Evaluation of Fuel Cell auxiliary Power Units for Heavy-Duty Diesel Trucks |year=2002 |publisher=Elsevier Sciences Ltd. |url=http://www.uctc.net/papers/587.pdf |work=Transportation Research Part D |pages=303–315 |access-date=2011-09-27 |archive-url=https://web.archive.org/web/20120403131809/http://www.uctc.net/papers/587.pdf |archive-date=2012-04-03 }}</ref> and uses diesel fuel more efficiently.<ref name="Weissler">{{cite journal | title = Delphi truck fuel-cell APU to hit road in 2012 | journal = Vehicle Electrification | date = 2010-05-12 | first = Paul | last = Weissler| url = http://ev.sae.org/article/8222 | access-date = 2011-09-27 | quote = and Delphi says it will have a 5-kW APU on the market in 2012. }}</ref> In 2008, a DOE sponsored partnership between Delphi Electronics and Peterbilt demonstrated that a fuel cell could provide power to the electronics and air conditioning of a Peterbilt Model 386 under simulated "idling" conditions for ten hours.<ref>{{cite news | first = Mike | last = Jacobs | title = Solid Oxide Fuel Cell Successfully Powers Truck Cab and Sleeper in DOE-Sponsored Test | date = 2009-03-19 | publisher = National Energy Technology Laboratory | url = http://www.netl.doe.gov/publications/press/2009/09017-Fuel_Cell_Powers_Commercial_Trucks.html | work = NETL: News Release | access-date = 2011-09-27}}</ref> Delphi has said the 5&nbsp;kW system for Class 8 trucks will be released in 2012,{{update inline|date=August 2015}} at an $8000–9000 price tag that would be competitive with other "midrange" two-cylinder diesel APUs, should they be able to meet those deadlines and cost estimates.<ref name="Weissler" />