The IAPAC Compressed Air Assisted Fuel Injection has been applied to the design and conception of a new 3 cylinder automotive 2-stroke engine of 1230 cc. This engine includes several innovations in addition to the IAPAC technology itself: fluid dynamically controlled combustion process (FDCCP), compactness with the block-integration of the IAPAC components, combined camshaft-balancing shaft, fixed exhaust port timing, … it presents particularly advantageous characteristics in terms of size and weight.The optimization of the different engine design parameters, before the installation of the engine in a vehicle, is presented in this paper. High engine trapping efficiency and smooth, stable and highly efficient light load auto-ignition combustion (ATAC) is controlled by the internal fluid dynamics.For the in-vehicle calibration, a fast catalyst lighting strategy has been implemented. The efficiency of this strategy combined with the low emissions light load auto-ignition combustion process allows the IAPAC demonstration vehicle to meet easily the European emissions legislation that will be valid up to the year 2000, with 20 % fuel consumption benefit and 20 % more low speed torque compared to an equivalent 4-stroke engine of the same power output. Complementary results concerning unregulated pollutants and potential for ultra low emissions are also presented.THE INVESTIGATIONS ON 2-STROKE ENGINES IN THE AUTOMOTIVE FIELD are seen as a way to replace the existing well-known 4-stroke engine by a lightweight, compact and highly efficient power unit. Several 2-stroke engine concepts for automotive application are under investigation or have been investigated all over the world [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20 and 21]. They have all the aim of retaining the benefits of all the 2-stroke cycle principle advantages while solving its drawbacks.IFP has accumulated expertise and know-how since 1980 in the field of the development of a new generation of clean and efficient 2-stroke engines. Among the new 2-stroke technologies developed and applied by IFP to 2-stroke engines, one of the most significant uses the original idea of crankcase Compressed Air Assisted Fuel Injection (named IAPAC, which stands for Injection Assistee Par Air Comprimé in French). This technology has been already developed and applied for a range of applications, from automotive [1, 2 and 3, 20] to marine outboard engines [22, 23 and 24, 27] and small displacement two-wheeler vehicles [25, 26 and 27].Recently, IFP decided to start the development of a demonstration IAPAC automotive 2-stroke engine. The aim of this demonstration is to validate in a running car the IAPAC fuel injection process combined with an innovative combustion process. This validation will allow to evaluate the potential of this solution for automotive application in terms of fuel economy, pollutant emissions, and vehicle driveability.Therefore the purpose of this paper is first, to present the new 2-stroke engine design and its main innovative features, second, to describe the engine direct fuel injection (DFI) and combustion process optimization and finally, to present the results obtained in a vehicle calibrated for the European emissions legislation.