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According to UN “58′ Agreement”, Yugoslavia is applying exhaust emissions ECE Regulations in three directions: vehicle type approval, conformity of production and control of vehicle in use. Approximately 95 % of Yugoslav engine and vehicle production has been covered by type approvals granted by Yugoslav Federal Institution for Standardization. However, test results show that over 50 % of approved vehicles are not more than 20 % below existing limits. Therefore, measures are undertaken to ensure conformity of production, though there are not enough data to judge emissions quality during production because of manufacturers lack of instrumentation. Emissions control of vehicles in use involves once a year regular inspection and periodic inspections in traffic. Inspections include idle CO for gasoline engines and free acceleration smoke for diesel engines, but incomplete results show unsatisfactory level of about 25 % vehicles over existing limits.

Turbocharging and intercooling were applied to a 1.1 1 passenger car gasoline engine in order to achieve power and torque of a 1.6 1 naturally aspirated engine. On the basis of standard production four cylinder OHC powerplant a prototype engine was developed featuring: turbocharger with integral wastegate, intercooler, pressurised carburettor and modified camshaft. Extensive dynamometer testing was carried out with the main objective to investigate effects of various design parameters on turbocharger system behaviour and to select optimum values for a desired power increase. Following parameters were varied: boost pressure level, temperature and pressure drop across intercooler, turbine housings and valve timing. Fuel economy comparison shows that turbocharged engine can be advantageous in the low load - low speed region.

Results from theoretical and experimental studies of cycle-by-cycle variations of flame propagation periods during the combustion in spark ignition engine are reported herein. Theoretical considerations show that cyclic variations depend on mixture turbulence and homogeneity characteristics. During an experimental work two ionization probes have been used to define the flame formation and total propagation periods and to enable visual observation of flame propagation duration in a series of successive engine cycles. The effects of main factors (turbulence level, compression ratio and mixture homogeneity) affecting flame kernel formation and flame propagation cyclic variations are discussed in the paper. One of the main conclusions is that a high turbulence reduces variations of developed flame propagation period, but an improved mixture quality could be important for the flame initiation. Both factors decrease total cyclic variations, though the effect of turbulence is greater.