Fuel Rail Pressure Rise during Cold Start of a Gasoline Direct Injection Engine
Gasoline direct injection provides reduced engine emissions, increased power, and increased fuel economy as compared to port fuel injection (PFI). Reduced emissions are largely due to starting the engine using high fuel pressure (up to 150 bar) and injecting into the compression stroke. During a cold start, fuel pressure must be increased from lift pump pressure (typically 4 to 6 bar) to desired injection pressure (typically 25 bar minimum). Start times are therefore impacted by the high pressure pump's ability to quickly build fuel pressure during crank. This study investigates the temperature and pressure affects during engine soak which allow vapor and air to form in the fuel system. Vapor and/or air in the system cause a slower fuel pressure build and increases start times. The scope of the problem and possible solutions were determined using theoretical and empirical testing. By preventing air and vapor formation in the fuel system, reduced and more consistent start times are achieved.
Analysis of NOx Emissions during Crank-Start and Cold Fast-Idle in a GDI Engine
The NOx emissions during the crank-start and cold fast-idle phases of a GDI engine are analyzed in detail. The NOx emissions of the first 3 firing cycles are studied under a wide set of parameters including the mass of fuel injected, start of injection, and ignition timing. The results show a strong dependence of the NOx emissions with injection timing; they are significantly reduced as the mixture is stratified. The impact of different valve timings on crank-start NOx emissions was analyzed. Late intake and early exhaust timings show similar potential for NOx reduction; 26-30% lower than the baseline. The combined strategy, resulting in a large symmetric negative valve overlap, shows the greatest reduction; 59% lower than the baseline. The cold fast-idle NOx emissions were studied under different equivalence ratios, injection strategies, combustion phasing, and valve timings. Slightly lean air-fuel mixtures result in a significant reduction of NOx. The engine-out emissions are highly sensitivity to combustion phasing. Initial retard results in lower mass NOx emissions up to CA50 around 40 °CA aTDC-compression. After this point the increase in fuel consumption and the reduction on residual fraction reverse the trend leading to an increase in NOx mass emissions for later combustion phasing. Moderate exhaust timing advance is beneficial for NOx emissions and has no impact on the exhaust enthalpy flow.
The Gospel and the land;: Early Christianity and Jewish territorial doctrine,
Ostensibly Davies' patient study of the concepton of the "land" (Israel, Jerusalem) in early Christianity is an essay in Biblical theology, but he also wishes to raise serious questions about Christian understanding (or misunderstanding) of Judaism. "Christians have usually understood Judaism in too theological, and therefore, too intellectual terms. And they have also looked at their own foundation document, the New Testament, in the same way. In their proper concern to unravel theological developments and subtleties in primitive Christianity, they have neglfected to search for evidences of an encounter between it and the realia of Judaism and for any possible resolutions of such an tencounter. In particular, they have failed to inquire after the place of the land in the thought and lives of early Christians" (p. 161). Davies observes, for example, that bible dictionaries often have no references whatsoever to "land" and those that do allot it but a few pages. Even in Old Testament scholarship, where the land is of central significance in the documents themselves, it has been neglected. His work is an attempt to provide a context of Jewish thinking from early Israelite writings up to the Talmud in which to place the Christian materials. The bulk of the book is an account of the historical and theological process by which early Christianity gave a "spiritual" interpretation of traditional Jewish views of the land. Read against the Jewish background, the radical spiritualizing of the tradition is striking. Yet Davies also shows that Jewish attitudes were not monolithic in the first century, that notions of a preexistent, heavenly or eschatological Jerusalem were present, and that some Jews considered the viability of Judaism apart from the land. At some point however what could be entertained as an abstraction in Judaism, when it was made concrete in the life of the Christian movement, could not be tolerated. The conflict was heightened, of course, by the destruction of Jerusalem and the continued existence of Christianity as a movement increasingly receptive to non-Jews. Christianity, however, while rejecting the link between the land and religion, did create a new sense of "holy space" by hallowing the places where Christ had been, a development which would find fullest expression some several centuries later. As a result of the Holocaust and the establishment of the modern state of Israel Christians are faced with a whole new series of issues which have lain dormant since the destruction of Jerusalem in A.D. 70. Davies' work must be read against this backdrop to appreciate its significance. It is as much a book about modern Christian thinking as it is about the past, as many of his citations and his several appendices of speeches at Jewish-Christian conferences show. To some it may appear that he has sided too closely with certain strands of Judaism and allowed this to color his way of handling the pre-Christian and pre-Rabbinic material, but such criticism is carping. Much of the material here is gathered together in this fashion for the first time, and he has successfully shown that a major preoccupation of ancient Judaism is missing in contemporary biblical scholarship. Further, he has given us a moving yet scholarly statement of the pathos of the modern Christian who cares about Christ and Israel and who tries to understand Israel while loving Christ.