Search Results

In two-stroke S.I. engines, direct fuel injection prevents fuel short-circuiting from the exhaust port, however it does not solve per se combustion problems at light loads due to excessive ratio of residual-to-fresh gas. These problems can be solved by ATAC (Active Thermo Atmosphere Combustion), since residual-gas thermal energy is used to prime the combustion of fresh gas. Experimental results of a small two-stroke S.I. engine with medium-pressure air-assisted fuel injection, operating on ATAC at light loads are shown and prove the possibility to combine the two solutions.

In two-stroke S.I. engines, direct fuel injection prevents fuel loss from the exhaust port, since only air is employed for the scavenging process. However, to solve the problem of combustion irregularity at light loads due to excessive presence of residual gas in the charge, fuel injection should also produce charge stratification. An alternative to stratification is ATAC (Active Thermo Atmosphere Combustion), which turns the effect of residual gas from negative to positive, since residual gas energy is exploited to prime the combustion of fresh gas. For the first time, the feasibility of ATAC combined with liquid high-pressure direct injection is proved in this paper. To illustrate the compatibility of ATAC with fuel injection, ATAC behaviours are shown in the cases of liquid high-pressure direct injection, air-assisted medium-pressure direct injection and indirect injection.

In two-stroke S.I. engines, direct fuel injection allows avoiding fuel loss from the exhaust port, since the cylinder is scavenged only with air. However, only if injection produces charge stratification, also combustion difficulties at light loads, due to the excessive presence of residual in the cylinder, can be removed. An alternative solution for this problem is ATAC (Active Thermo Atmosphere Combustion), which turns the effect of residual gas from negative to positive, since its thermal energy is used to prime the combustion of fresh gas. ATAC leads to very good combustion stability with small cycle-to-cycle variation and to good fuel economy and low exhaust emissions of unburned hydrocarbons. This paper deals with ATAC combined with direct fuel injection, both of the air-assisted medium-pressure type and of the liquid high-pressure type.

Direct fuel injection is becoming mandatory for two-stroke S.I. engines, since it allows using only air in the scavenging process, preventing fuel loss from the exhaust port. However, also combustion irregularity at light loads is a problem of these engines, due to excessive presence of residual gas in the charge. For its solution, additional strategies must be adopted. The two most suitable ones are charge stratification and ATAC (Active Thermo Atmosphere Combustion), which makes use of residual gas energy to ignite fresh gas, turning the effect of residual gas from negative to positive. In previous papers, the possibility of combining ATAC with different injection systems was proved. This paper provides further insight on ATAC combined with liquid high-pressure direct injection and shows the studies and the first experimental results relative to charge stratification.