UTS study details efficiency benefits of combining ethanol direct injection with gasoline port injection
|Variation of indicated thermal efficiency with increased EER at 3500 rpm and light load. Zhuang and Hong, 2013. Click to enlarge.|
A new study by researchers at the University of Technology, Sydney (Australia) is contributing more detail on the leveraging effect of combining ethanol direct injection with gasoline port injection (EDI + GPI) to reduce gasoline consumption in a spark ignition engine while retaining performance. (The EDI + GPI concept was proposed by MIT researchers in 2005. Earlier post.)
Existing methods of using ethanol fuel—e.g., in blends with gasoline or neat—do not make the best use of ethanol’s potentials in improving engine performance, they noted in a paper on their work in the journal Fuel. Ethanol possesses a higher octane number and latent heat of vaporization, which allow the use of higher compression ratios and consequently can lead to the increased thermal efficiency. Ethanol fuel’s higher combustion velocity could also help increase the combustion efficiency and minimize the energy loss.
Aiming to leverage the effect of the available ethanol in reducing the consumption of gasoline fuel, Cohen et al. first proposed direct injection of ethanol fuel in developing a small turbocharged SI engine which should match the performance of a much larger existing engine. In their report, they estimated ethanol's energy value increased by the leveraging effect on increasing the efficiency of using gasoline fuel...Their experimental results showed that the engine thermal efficiency could be improved and the ethanol fuel could be used to conserve gasoline usage.
...Investigation to dual-injection strategies applied to SI engines has been reported in the past 2 years...This paper reports our preliminary results of investigating the leverage effect of using ethanol fuel on reducing the consumption of gasoline fuel and on improving engine performance of a single cylinder research engine equipped with EDI + GPI. The results include the effect of ethanol fuel energy ratio on the engine performance such as BMEP, volumetric efficiency, fuel consumption, in cylinder pressure, indicated thermal efficiency and emissions.
The UTS team, Yuan Zhuang and Guang Hong, used a modified single-cylinder motorcycle engine (Yamaha YBR250). The engine was equipped with an electronic control unit (ECU), a direct injection system for ethanol, and a port injection system for gasoline. Port fuel injection pressure was 250 kPa, and the pressure in the common rail for direct injection was adjustable to be a fixed value in the range of 3-13 MPa. Gasoline for the test was supplied by BP Australia with a research octane number (RON) of 95; the ethanol’s RON is 106.
Experiments were conducted at light and medium engine loads with engine speed varied from 3500 to 5000 rpm at 500 rpm intervals. At each engine load condition, the total energy input value (ethanol + gasoline) was fixed, and the ethanol/gasoline energy ratio (EER) was varied from 0%—i.e, gasoline only—to 60.1%. EDI pressure was fixed at 4 MPa when EER was less than or equal to 48.3% and 6 MPa when EER was greater than 48.3%
(EER for the paper is defined as the rate of the heating energy (HE) of the ethanol divided by the rate of the total heating energy of ethanol and gasoline fuels. The rate of heating energy is equal to the fuel mass flow rate multiplied by the lower heating value (LHV) of the fuel.)
Spark timing and ethanol injection timing were fixed at 15 crank angle degrees (CAD) BTDC and 300 CAD BTDC respectively. The 300 CAD timing was selected to provide sufficient time for the ethanol and fresh charge from the intake port to mix, resulting in a homogeneous mixture for combustion.
Among the results of increasing EER were:
Increased BMEP and volumetric efficiency. This indicates that to achieve the comparable engine brake power, less energy input would be required in an SI engine equipped with EDI and GPI—i.e., gasoline fuel consumption for equivalent performance could be reduced by leveraging the use of ethanol.
Increased maximum in-cylinder pressure increased and reduction in CA50, showing that the engine expansion work increased when the ratio of ethanol to gasoline was increased. Consequently, indicated thermal efficiency increased.
NO emissions decreased and CO and HC emissions increased. The team suggested that the reduced NO could be due to the in-cylinder temperature reduced by directly injected ethanol fuel greater than that of port-injected ethanol gasoline. The increase of CO and HC emissions could be attributed to the relatively low in-cylinder temperature, leading to incomplete combustion.
The leveraging effect of ethanol fuel on improving engine performance could be attributed to factors such as the cooling effect of ethanol directly injected into the combustion chamber, the LHV of the stoichiometric mixture per unit mass of air increased with EER, mole multiplier effect and ethanol's high combustion velocity.—Zhuang and Hong
Yuan Zhuang, Guang Hong (2013) Primary investigation to leveraging effect of using ethanol fuel on reducing gasoline fuel consumption, Fuel, Volume 105, Pages 425-431, doi: 10.1016/j.fuel.2012.09.013