| UN R143 HD Dual Fuel Retrofit Systems | Heavy-Duty Dual Fuel Retrofit Systems | Uniform provisions concerning the approval of Heavy Duty Dual-Fuel Engine Retrofit Systems (HDDF-ERS) to be installed on heavy duty diesel engines and vehicles HD Dual Fuel Retrofit Systems Heavy-Duty Dual Fuel Retrofit Systems UN Regulation No. 143 UN R143 | UNR | 143 |