Paul Brian Edward Connelly, 51, of Burnie, was found guilty of two counts of attempted murder in December 2013.

Connelly had been sent to jail for 20 years, with a 15 year non-parole period, but is appealing against his sentence.

His lawyer, Tamara Jago, SC, told the Court of Criminal Appeal in Hobart yesterday that Connelly’s sentence was ‘‘disproportionate to the appellant's offending on a whole, and demonstrates error’’.

Connelly had 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.

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 multiple operations.

At the time of his sentence, Chief Justice Alan Blow said Connelly decided to kill the boys, aged 5 and 8, to spite his wife.

Ms Jago told the court while Connelly’s conduct was ‘‘most grave’’, the 15-year non-parole period was ‘‘manifestly excessive’’ and the 20-year sentence was ‘‘exceptionally heavy’’.

She said the jail time was longer than other sentences for attempted murder in Tasmania.

Acting Director of Public Prosecutions Darryl Coates, SC, said Connelly’s crimes were ‘‘horrendous’’ and he had shown no remorse.

Mr Coates said the premeditated crimes caused ‘‘horrific scenes’’ for those who came to help, and the children suffered ongoing anxiety and trauma.

‘‘It could not be said that this was outside the range of permissible sentences in this case,’’ Mr Coates said.

The full bench of the Court of Criminal Appeal adjourned to make a decision at a later date.