Some reading material:

http://www.eere.energy.gov/afdc/apps/toolkit/pdfs/mod05_lpg.pdf
http://www.ilovesponge.com/spongecars/diesel/dieseltechnical.htm
http://www.cummins.com/na/pdf/en/products/4103537.pdf
http://www.boostlpg.co.uk/what_is/faq.htm
http://www.chilterngascars.co.uk/cars/lpgdiesel.htm