A 51-year old woman died in a mobile home fire in Lowell early Tuesday, fire officials said. The one-alarm blaze broke out around 1:45 a.m. on Billerica Street and was put out within 20 minutes, said Lowell Deputy Fire Chief Jeff Winward. He said two other occupants of the mobile home escaped without injury. Officials did not identify the victim. “Evidence is pointing to the fact that this was an accidental fire,” said Winward. “But our investigation is ongoing.” No smoke alarms were installed in the home, said Jennifer Mieth, a spokeswoman for the state fire marshal. It was the fifth deadly fire in the state this year, Mieth said.