An attempt has been made to study the combustion and emission characteristics of ultra-low diesel fuel for high speed direct injection ( HSDI) diesel engine at different fuel injection timings( -12,-9,-6,-3,0 )ATDC . The fuel injection pressure was 800 bar and at high load ( 80Nm= 5BMAP) , low load ( 40Nm=2.5BMAP ) , With constant engine speed ( 1500rpm) . In-cylinder pressure was measured and then analyzes this pressure using LABVIWE program and calculation program in MATLAB software to extract the apparent heat release rate, the ignition delay, combustion duration and the amount of heat released during the premixed and diffusion combustion phases . The influence of injection timing on the exhaust emissions such as carbon monoxide (CO), total hydrocarbons (THCs), nitric oxides (NOx), smoke number (SN) and fuel consumption were also investigated. A result referring to that the retardation of the injection timing lead to increase the ignition delay and therefore the premixed burn fraction which plays a key role in the combustion and emission characteristics .this leads to change combustion mode to low temperature combustion at late injection timing.

هذاالبحث دراسة لخصائص الاحتراق والانبعاثات لوقود الديزل منخفض الكبريت باستخدام محرك ديزل عالي السرعة وذوحقن مباشر ومع تغييرتوقيت الحقن عند 0,-3,-6,-9,-12 ATDC )) ,ضغط الحقن للوقود كان 800barواجريت التجارب عند الحمل العالي (80Nm=5BMEP) والحمل المنخفض( 40Nm=2.5BMEP), تم تثبيت سرعة المحرك عند 1500 rpm .تم قياس الضغط داخل غرفة الاحتراق ومن ثم تحليل هذا الضغط باستخدام برنامج LABVIWE وبرنامج حسابي باستخدام برنامج MATLAB لحساب معدل الحرارة المنطلقة وتاخر الاشتعال ومدة الاحتراق وكمية الحرارة المنطلقة فيطور الاحتراق المسبق الخلط وكذلك فيطور الاحتراق الانتشاري. تاثير توقيت الحقن على انباعاث الغازات العادم مثل اول اوكسيد الكاربون (CO) الهادر وكابون غير المحترق الكلي (THC) واكاسيد الناتروجين ( NOx) ورقم الدخان (SN) ومعدل استهلاك. النتائج اشارة الى ان تاخير توقيت الحقن يؤدي الى زيادة تاخير الاشتعال وبالتالي زيادة كمية الاحتراق المسبق الخلط والذي يلعب الدور الرئيسي في تحديد خصائص الاحتراق والانبعاثات . وذلك يمكن ان يؤدي الىتغيير طبيعة الاحتراق الى احتراق منخفض درجة الحرارة عندما يكون توقيت الحقن متاخر .

combustion --- diesel engine --- injection pressure --- gases emissions

The present work investigates the influence of fuel injection pressure on the combustion and emission characteristics of ultra-low diesel fuel for high speed direct injection ( HSDI) diesel engine at different fuel injection timings( -12,-9,-6,-3,0 )ATDC has been made . The fuel injection pressure were (800,1000,1200) bar and at high load ( 80Nm= 5BMAP) , low load ( 40Nm=2.5BMAP ) , With constant engine speed ( 1500rpm) . In-cylinder pressure was measured and analyzed using LABVIWE program .A calculation program specially written in MATLAB software was used to extract the apparent heat release rate, the ignition delay, combustion duration and specifies the amount of heat released during the premixed and diffusion combustion phases ( premixed burn fraction PMBF) and ( diffusion burn fraction DBF). The influence of injection pressure on the exhaust emissions such as carbon monoxide (CO), total hydrocarbons (THCs), nitric oxides (NOx), smoke number (SN) and fuel consumption were also investigated.A result referring to that when the injection pressure was increased, the ignition delay reduced. A shorter ignition delay at high injection pressure also advanced the combustion, and increased the in-cylinder pressure, heat release rate and their peaks respectively .The premixed burn fraction increased with fuel injection pressure increasing, and this caused a decrease in each of the exhaust SN, THC and CO emissions but the NOx emissions increased.

combustion --- diesel engine --- injection pressure --- gases emissions