The white smoke generated by a diesel engine was analyzed and found to consist mainly of hydrocarbons. Test results indicated that the emission level depends on ambient temperature. A compact white smoke meter was developed to enable emission levels to be accurately measured. The internal temperature of this meter is controlled so that white smoke is generated within the measuring device. The meter was used to evaluate the effectiveness of various white smoke emission control devices for the DI diesel engine. The results indicated that an intake air heater offers the greatest potential. Accordingly, a new intake air heater with ceramic PTC thermistor having a very high heating efficiency was developed to reduce white smoke emission.