Search Results

In this work, a promising technique, consisting of a liquid Water Injection (WI) at the intake ports, is investigated to overcome over-fueling and delayed combustions typical of downsized boosted engines, operating at high loads. In a first stage, experimental tests are carried out in a spark-ignition twin-cylinder turbocharged engine at a fixed rotational speed and medium-high loads. In particular, a spark timing and a water-to-fuel ratio sweep are both specified, to analyze the WI capability in increasing the knock-limited spark advance. In a second stage, the considered engine is schematized in a 1D framework. The model, developed in the GT-Power™ environment, includes user defined procedures for the description of combustion and knock phenomena. Computed results are compared with collected data for all the considered operating conditions, in terms of average performance parameters, in-cylinder pressure cycles, burn rate profiles, and knock propensity, as well.

Nowadays different technical solutions have been proposed to improve the performance of internal combustion engines, especially in terms of Brake Specific Fuel Consumption (BSFC). Its reduction of course contributes to comply with the CO2 emissions legislation for vehicle homologation. Concerning the spark ignition engines, the downsizing coupled to turbocharging demonstrated a proper effectiveness to improve the BSFC at part load. On the other hand, at high load, the above solution highly penalizes the fuel consumption mainly because of knock onset, that obliges to degrade the combustion phasing and/or enrich the air/fuel mixture. A promising technique to cope with the above drawbacks consists in the Variable Compression Ratio (VCR) concept. An optimal Compression Ratio (CR) selection, in fact, allows for further improvements of the thermodynamic efficiency at part load, while at high load, it permits to mitigate knock propensity, resulting in more optimized combustions.