Cambridge firm scores big backing to produce mystery ethanol-maker. Alternative fuel maker Joule Unlimited Inc. has raised $30 million in venture funding, the largest such deal this year for a clean technology company in New England, according to the National Venture Capital Association. The company, which is based in Cambridge, declined to name the investors, but said the money will be used to help produce its fossil fuel substitutes in larger quantities. Formerly known as Joule Biotechnologies, the firm said it will also begin making what chief executive Bill Sims described as a “high quality’’ diesel fuel.