Converting a Small Car to LNG: What Are the Problems and What Can It Do for Economy and Emissions?

A two litre compact car originally designed to run on gasoline has been converted to run on LNG. Comparative measurements of fuel economy and exhaust emissions were made for the same car running on each fuel under normal on-the-road and simulated taxi service. When tuned to its maximum economy configuration the LNG car gave significant improvements in fuel economy when expressed on an energy basis. For inter-urban journeys the savings would be of the order of 5% and for taxi type service in excess of 20%. Whether or not these savings would justify fleet conversion would depend on local fuel cost and taxation conditions.

When set for maximum economy the LNG car gave significantly lower emissions of CO and hydrocarbons than its gasoline counterpart. Emissions of NO_x were, however, higher with LNG than with gasoline. A tenfold reduction in NO_x emissions could be obtained by re-tuning the LNG engine to run at air/fuel ratios up to 30:1. Hydrocarbon emissions with this configuration were, however, quite high and would require supplementary means of control. When tuned to operate at very weak mixtures the car remained quite driveable but was 10 to 15% less economical than when tuned for maximum economy.

Although technically practical, the use of LNG is likely to be restricted by supply and distribution limitations to fleet operators and other high mileage users who could refuel from centralized points where trained staff would be available.