Paul Brian Edward Connelly, 50, of Burnie, barely blinked under his burns mask as his sentence was handed down by Chief Justice Alan Blow in Hobart's Supreme Court.

Connelly told the children they would have a picnic in the car, and put two gas bottles in the rear of the vehicle and ignited them after the gas leaked out.

In handing down his sentence, Chief Justice Blow said Connelly decided to kill the boys aged 5 and 8 in order to spite his wife.

The judge said this was an attempted murder worse than most others, and that there were two victims who received life threatening injuries and will have ongoing and intense treatment.

Chief Justice Blow said as their father, Connelly had a duty to protect the boys.

``Attempting to kill them involved the worst possible breach of trust,'' he said.

Connelly had arranged for his wife to collect the children from his house.

``I infer that he intended that she would turn up to collect them, and find that they had been burned to death,'' he said.

Both children received full thickness burns to up to 30 per cent of their bodies and spent months in the Royal Children's Hospital, and have had 13 operations to date. 

``From psychological, social and emotional perspectives each of the boys has had an extraordinarily traumatic experience.''

Connelly was convicted on both charges of attempted murder and sentenced to 20 years' jail, effective from January 3, 2014.